HESI A2 ENTRANCE CHEMISTRY EXAM 2023 QUESTIONS &ANSWERS LATEST UPDATES

HESI A2 ENTRANCE CHEMISTRY EXAM 2023 QUESTIONS &ANSWERS LATEST UPDATES HESI A2 CHEMISTRY V1/V2 FILE 1. If a Hydrogen isin a compound, what would its oxidation number be? +1 2. What isthe oxidation number of any simple ion? +1 or -1 depending on the charge of the ion 3. How many kilograms are in a pound? 0. kg 4. What is the temperature for freezing point of water in Celsius? 0 degrees Celsius (32°F for Fahrenheit) 5. What is the conversion of Celsius to Fahrenheit? 0°C = 32°F 6. What is the oxidation number of an element atom? 0 7. What is the freezing point of sea water in Fahrenheit? 0°F 8. How many amino acids are in a dipeptide? 2 9. If Oxygen is in a compound, what would its oxidation number be? -2 10. Which of the following pH values would lemon juice likely have? 2 because the lower the pH value, the more acidic 11. What is a pentose? A 5 carbon sugar (Pent = 5) (ose = sugar) 12. What is the oxidation state of the Sulfur atom in Sulfuric Acid H2SO4? 6 13. How many neutrons does carbon 14 have? 8 ( mass# - atomics # = neutrons) 14 - 6 = 8 14. How many protons does Potassium have? 19 15. How many amino acids are essential for human life? 20 amino acids 16. Normal body temperature in °C? 37°C 17. Normal body temperature in °F? 98.6°F 18. Boiling point of water in °C? 100°C 19. Boiling point of water in °F? 212°F 20. 0°K is equal to °C? -273°C 21. The term Amphoteric means? A substance that can act as both a base & acid 22. What is Kelvin based around? Absolute zero 23. A compound that is a Hydrogen or proton donor, corrosive to metals, causes blue litmus paper to become red and becomes less acidic when mixed with a base is? Acid 24. Mixture of 2 or more metals are? Alloys 25. Acids: 33. Atomic #: # of protonsin nucleus of an atom 34. Base? • A Hydrogen or proton ACCEPTOR & has hydroxide group in the makeup of the molecule 26. 27. pH less than 7.0 sour/tart Formulas begin with H (Hydrogen) Proton Donor 3 types of radiation in nuclear chemistry? Alpha, Beta & Gamma Alpha radiation: * Emission of Helium (He) ions in the nuclei * Contains 2 protons & 2 neutrons. * +2 Charge * Largest radiation particle. * Can be stopped by piece of paper 00. Type of Alloy in which another metal is dissolved in Mercury (Hg)? Amalgam 28. Proteins are made up of? Amino Acids 29. Glycogen is what kind of starch? Animal Starch 30. When a electron gains one or more electrons? Anions 31. Basic building block of a molecule? Atom (NOT CELL!!) 32. Atomic mass? Average mass of a elements isotope • Produce -OH • Bitter,slippery, conduct electricity, formulas contain -OH • pH value greater than 7.0 • Proton acceptor 35. Key note: Acids are Proton donors as Bases are proton acceptors 36. Beta radiation: • Decomposition product of a proton or neutron • High speed/energy Electrons • EITHER - charged electrons or + charged positrons • Can be stopped by aluminum foil 37. What is Biochemistry? Study ofsubstances & processes occurring in living things 38. Fahrenheit is based off of? Body temperature 39. How does ↑ Surface area speed up chemical reactions? By ↑ areas of contact where chemical reactions can occur 40. How do catalyst accelerate a chemical reaction? By reducing the amount of energy needed for a reaction to occur 41. What does COOH symbolize? A Carboxyl group 42. Which of the following is not a solution type? Catalyst 43. Define Catalyst. Substance that speeds up a chemical reaction. 44. What is an atom called when it LOSES 1 or more electrons? Cations 45. What is chemical bonding? The joining of atomsto form new substances. 2 types: ionic & covalent bonding 46. What is a Ionic bond? • Electrical attraction between 2 oppositely charged atoms groups of atoms called ions • (between metals &nonmetals) 47. Ionic bonding? Chemical bond that’sformed when an atom transfers a electron to another atom. (steals) 48. Single Covalent bond? • Chemical bond that shares 1 electron pair • Formed by non-metals 49. What are chemical reactions? Making & breaking of chemical bonds, leading to changes in composition of matter 50. Double Covalent bond? When 2 electron pairs are shared 51. Triple Covalent bond? When 3 electron pairs are shared 52. The following is an example of? Combustion reaction 2C2H6 (g) + 7O2 (g)  4CO2(g) + 6H2O 53. What is a combustion reaction? A chemical reaction that occurs when a substance reacts with Oxygen, releasing energy in the form of heat & light 54. What is a compound? • Combination of 2 or more elements or atoms. • Made up of atoms of 2 or more different elementsjoined by chemical bonds 55. Different types of solutions? Compounds, Alloys, Amalgams, Emulsions 56. Strongest type of chemical bond? Covalent 57. What is a decomposition reaction? A SINGLE compound breaks down to form 2 or more simpler substances 58. What is Deoxyribose? A sugar used in the formation of DNA 59. Attractions between opposite charges of polar moles? Dipole-dipole forces 60. What is a Disaccharide? A double sugar molecule made of 2 monosaccharides bonded together through dehydration synthesis. 61. When 2 monosaccharides are joined together this makes? Disaccharide 62. Type of chemical bond that share 2 electron pairs? Double covalent bond 63. Example of double replacement? AB + CD = AD + CB 64. Example of Single replacement? A + BC  B + AC 65. Group of electrons revolving around the nucleus of an atom, or known as a cloudlike group of electrons? Electron clouds 66. Mixtures of matter that readily separate such as water and oil? Emulsion 67. 3 common temperature systems? Fahrenheit, Celsius, Kelvin 68. Celsius is based around? Freezing &boiling point of water 69. What is reduction? GAIN of electrons 70. Gamma radiation: • Similar to xrays • Can be stopped by several feet of concrete or several inches of Lead • High energy electromagnetic radiation lacking charge and mass 71. Unit measure of weight? Gram 72. Basic units of METRIC system? Gram, Liter Meter 73. What are Hydrogen bonds? Weak attraction between a hydrogen atom & another atom 74. Examples of intermolecular forces? Hydrogen bonds, dipole-dipole, dispersion forces 75. 4 basic ways to speed up a reaction? ↑ temperature, ↑ Surface area, ↑ catalyst & concentration 76. What are intermolecular forces? Forces of attractions between molecules 77. Where are nucleic acids, DNA & RNA found? Cell nucleus 78. Atoms of the same element but have different numbers of neutrons? Isotope 79. Gluconeogenesis is a process that produces? Glucose from proteins and fats 80. What is oxidation? Loss of electrons(OIL) 81. A way to express concentration of atoms? Mole 82. What is reduction? Gain in electrons(RIG) 83. Part of the nucleus of an atom that has no charge? Neutron 84. What is the Molarity Formula? Moles of SoluteLiters of Solution=Molarity 85. Single sugar molecules? Monosaccharides 86. How does ↑ concentration cause reaction acceleration? More potential for contact (chemical reaction) 87. Which is a example of a ionic bond? NaCl (Sodium Chloride) because it does not have a charge 88. In a covalent bond compound, if the electrons are shared equally, then the bond is? Non-polar (water loving, equal) 89. The study of changes that occur in atomic nuclei? Nuclear Chemistry 90. Polar Covalent bond? Unequalsharing of electrons 91. When 3-6 monosaccharides join together this is called? Polysaccharide 92. Emission of particles or energy from a unstable nucleus? Radioactivity 93. Particles that are emitted during radioactivity? Radiation 94. Ractant is? A chemical substance that is present at the start of a chemical reaction. Reactant  Product 95. A substance that is dissolved in a solution? Solute 96. A homogenous mixture of 2 or more substances? Solution 97. Liquid substance capable of dissolving other substances? Solvent 98. Define stoichiometry. Calculation of quantities in chemical reactions 99. Combining parts into a whole is? Or synthesis is? • Synthesis • Chemical reaction in which 2 elements combine to form a product 100. How many electrons does an Oxygen ion have? 10 (Atomic # of 8 & is in group VIA which has a -2 charge, which means it has 2 more electrons than the 8 protons) 101. What is the charge of Potassium (K) in KCl? +1 because K isfound in group IA 1. What is the mass of 1 mole of CO2? 44g/mol (C =12.011 + (15.999 x 2) = answer 2. How many moles are present in 2 moles of O2? 3. 1.204 x 1024 ( 1 mole – 6.02 x 1023) 2 mole would be double that 4. What characterizes a chemical reaction as combustion? The chemical reaction that is the reaction of a compound with Oxygen? • Adding O2 • Combustion 5. Sum of oxidation # =? Charge on polyatomic ion 6. Increasing the causes the particles to have greater kinetic energy, allowing them to move faster and have a greater chance? Temperature 7. To balance an equation, what are placed in front of each component? Coefficient 8. Dispersions forces are found in which covalent bond? Non-polar 9. The weakest of all intermolecular forces? Dispersion forces 10. A Dipole attraction is a intermolecular force? Weak 11. What is created when an electron pair in a covalent bond is shared unequally? Dipole 12. The attractions of one dipole to another is? Dipole interactions 13. Strongest bond of intermolecular forces? Hydrogen bond. (This is not relating to covalent) 14. Elements Flourine (F), Chlorine (Cl ), Oxygen (O) and Nitrogen (N) are involved in which bond? Hydrogen bond 15. Polarity is? Based on the difference in electronegativity values for the elements involved 16. What reactionstake p[lace in the nucleusto obtain stable nuclear configurations? Nuclear reactions 17. Mass # - Atomic # = # Neutrons in a element 18. Protons + Neutrons = Mass # 19. # of Protons in a element = Atomic # 20. Neutral ions = Neutrons 21. – charge ions = electrons 22. + charge ions = Protons 23. Charge of noble gases? 0 24. Group IA = +1 Charge 25. Group IIA = +2 Charge 26. Group IIIA = +3 Charge 27. Group VA = -3 Charge 28. Group VIA = -2 Charge 29. Group VIIA = -1 Charge 30. Rows on periodic table: Period (Horizontal Left/right) 31. Columns of periodic table: Group (Vertical up/down) 32. Mass # - Atomic # = # Neutrons in a element 33. # protons an element has: Atomic # 34. How elements are arranged on the periodic table? By their chemical properties 35. Matter that has definite shape & volume? Solid 36. Matter that changes in volume with changes in temperature & pressure? Gas 37. Which change of matter is when no change is made to the chemical composition of a substance? Physical 38. Simplest substance and is represented by a letter or letters? Element 39. Law that states matter can neither be created nor destroyed during a chemical reaction? Law of conservation of mass Chemistry 1. What are all metric measurements composed of? A. Metric prefix and a basic unit of measure B. A significand and a metric prefix C. A metric prefix and a coefficient D. A coefficient and a significand 2. What is the most commonly used temperature scale in the scientific community? A. Fahrenheit B. Celsius or Centigrade C. Kelvin D. English temperature method 3. The nucleus of an atom contains or is made up of which of the following? A. Protons and electrons B. Protons only C. Protons and neutrons D. Neutrons and electrons 4. What is an atom that has a positive charge called? A. A cathode B. A cation C. An anode D. An anion 5. In the periodic table, what are the rows called? A. Groups Number of neutrons Number of protons Number of electrons Number of isotopes Which of the following describes the atomic mass? Mass of protons and electrons Mass of neutrons and electrons Average mass of that element’s isotopes Number of moles in a solution Chemical equations are written in which manner? Product → Reactants Reactants → Products Reactants + Reactants Products + Reactants What is the charge on potassium in the compound KCl? −1 B. Moles C. Columns D. Periods 6. What is the atomic number? A. B. C. D. 7. A. B. C. D. 8. A. B. C. D. 9. A. B. +1 C. −2 D. +2 10. A catalyst is a substance that accelerates a reaction by which of the following? A. Adding energy to the overall reaction B. Increasing the amount of energy needed for the reaction to occur C. Finding an alternate pathway for a reaction that requires less energy D. Speeding up the overall reaction process 11. Percent concentration of a solution is expressed as which of the following? A. 100 parts per 100 dL B. Parts per 100 parts C. Parts of moles D. Moles per 100 parts 12. What will one liter of a one molar solution of any element contain? A. The atomic mass in grams of that element B. The atomic number in grams of that element C. The atomic mass in liters of that element D. The atomic number in liters of that element 13. Chemical bonding is the bonding of which of the following? A. One atom to another atom B. One mole to another mole C. A proton to an electron D. One cation to another cation 14. Which of the following describes an ionic bond? A. It shares electrons. B. It does not share electrons. C. It is sometimes called a covalent bond. D. It is the strongest of all chemical bonds. 15. The reaction 2C2H6 + 7O2 → 4CO2 + 6H2O has a ratio of 2 parts ethane (C2H6) and 7 parts oxygen (O2). How many parts of ethane (C2H6) will be needed to react with 21 parts of oxygen (O2)? A. 3 parts of ethane C2H6 B. 6 parts of ethane C2H6 C. 9 parts of ethane C2H6 D. 14 parts of ethane C2H6 16. What is the concentration of 58.5 g of NaCl in 2 L of solution (atomic weights of each element are as follows: Na = 23 g/mol, Cl = 35.5 g/mol)? A. 0.5 mol NaCl B. 0.75 mol NaCl C. 1 mol NaCl D. 2 mol NaCl 17. In a redox reaction, which of the following describes reduction? A. It is the loss of electrons. B. It is the gain of protons. C. It is the loss of a neutron. D. It is the gain of electrons. 18. What are acids? A. Hydrogen acceptors B. Solutions of high pH C. Hydrogen donors D. Amphoteric 19. What is a benefit of water’s ability to make hydrogen bonds? A. Lack of cohesiveness B. Low surface tension C. Use as a nonpolar solvent D. High specific heat 23. Which is the correct way to write Iodine (I) with an atomic mass of 131? A. I131 B. I131 C. 131I D. 131I 20. A. B. C. D. What are bases or alkaline solutions? Hydrogen acceptors Solutions of low pH Hydrogen donors Amphoteric 21. Chemical reactions in living systems proceed along catabolic pathways, and there tends to be an increase in which of the following? A. B. C. D. Entropy Enthalpy Glucose Glycogen 22. A. B. C. D. What is a pH of 7? Acidic Basic Neutral Positive 24. What is the correct formula for magnesium chloride? A. MgCl2 B. MgCl C. Mg2Cl D. Mg2Cl2 25. What is the weakest of all the intermolecular forces? A. Dispersion B. Dipole interactions C. Hydrogen bonding D. Covalent bonding 26. Beta radiation is the emission of which of the following? A. Large numbers of helium ions B. An electron C. High energy electromagnetic radiation D. A product of the decomposition of a proton 27. Which of the following describes carbohydrates? A. They serve as fuel for the body. B. They are present in DNA but not in RNA. C. They are the least abundant biomolecule. D. They cannot be stored in the body. 28. What are monosaccharides? A. The simplest form of carbohydrates B. The most complex form of carbohydrates C. One form of a very complex fat D. Artificial sweeteners such as saccharin 29. Disaccharides are the joining together of which of the following? A. Three to six monosaccharides B. Two monosaccharides C. A number of monosaccharides D. A fat and a monosaccharide 30. Glycolysis is one of the body’s chemical pathways for which of the following? A. Manufacturing glycogen B. Building proteins C. Producing fats D. Metabolizing glucose 31. Amino acids are the building blocks for which of the following? A. Nucleic acids B. Carbohydrates C. Proteins D. Lipids 32. What is the union of two amino acids using a peptide bond called? A. A dipeptide B. A peptide C. A monopeptide D. A polypeptide 33. Which of the following describes lipids? A. They are a major source of fuel for the body immediately after a meal. B. They are stored for a source of fuel after carbohydrate depletion. C. They are comprised of glycerol and three fatty acids. D. They are metabolized by a pathway called glycolysis. 34. Which of the following describes DNA? A. It is made of two strands of a ribose sugar-phosphate chain. B. It consists of two strands of a deoxyribose sugar-phosphate chain. C. It consists of one strand of a ribose sugar-phosphate chain. D. It is located solely in the mitochondria of individual cells. 35. Use of the periodic table allows prediction of which of the following? A. The properties of each of the elements B. The charge of polyatomic ions C. The number of isotopes in each element D. The potential for discovery of new elements 36. How could water be boiled at room temperature? A. By lowering the pressure B. By increasing the pressure C. By decreasing the volume D. By raising the boiling point 37. What is a combustion reaction? A. It is endothermic. B. It substitutes one element for another. C. It always shares electrons. D. It is a reaction that involves oxygen. 38. What is KCl → K + Cl2 an example of? A. Synthesis B. Decomposition C. Single replacement D. Double replacement 39. Iodine and carbon dioxide undergo sublimation at room temperature and atmospheric pressure. What is this process? A. Changing from a gas to a solid B. Changing from a liquid to a gas C. Changing from a solid to a liquid D. Changing from a solid to a gas 40. An experiment is performed to measure the temperature of boiling water at sea level. The actual boiling point is 104.6° C, 104.5° C, and 104.4° C. What term best describes these data? A. Accurate B. Precise C. Variable D. Equivalent Chemistry Questions with Answers and Explanations 1. Which of the following substances allows for the fastest diffusion? A. gas B. solid C. liquid D. plasma Explanation: Diffusion is fastest through gases. The next fastest medium for diffusion is liquid, followed by plasma, and then solids. In chemistry, diffusion is defined as the movement of matter by the random motions of molecules. In a gas or a liquid, the molecules are in perpetual motion. For instance, in a quantity of seemingly immobile air, molecules of nitrogen and oxygen are constantly bouncing off each other. There is even some miniscule degree of diffusion in solids, which rises in proportion to the temperature of the substance. 2. What is the oxidation number of hydrogen in CaH2? A. +1 B. 1 C. 0 D. +2 Explanation: The oxidation number of the hydrogen in CaH2 is –1. The oxidation number is the positive or negative charge of a monoatomic ion. In other words, the oxidation number is the numerical charge on an ion. An ion is a charged version of an element. Oxidation number is often referred to as oxidation state. Oxidation number is sometimes used to describe the number of electrons that must be added or removed from an atom in order to convert the atom to its elemental form. 3. Which of the following does not exist as a diatomic molecule? A. boron B. fluorine C. oxygen D. nitrogen Explanation: Boron does not exist as a diatomic molecule. The other possible answer choices, fluorine, oxygen, and nitrogen, all exist as diatomic molecules. A diatomic molecule always appears in nature as a pair: The word diatomic means “having two atoms.” With the exception of astatine, all of the halogens are diatomic. Chemistry students often use the mnemonic BrINClHOF (pronounced “brinkelhoff”) to remember all of the diatomic elements: bromine, iodine, nitrogen, chlorine, hydrogen, oxygen, and fluorine. Note that not all of these diatomic elements are halogens. 4. What is another name for aqueous HI? A. hydroiodate acid B. hydrogen monoiodide C. hydrogen iodide D. hydriodic acid Explanation: Hydriodic acid is another name for aqueous HI. In an aqueous solution, the solvent is water. Hydriodic acid is a polyatomic ion, meaning that it is composed of two or more elements. When this solution has an increased amount of oxygen, the -ate suffix on the first word is converted to -ic. The HESI exam will require you to know the fundamentals of naming chemicals. This process can be quite complex, so you should carefully review this material before your exam. 5. Which of the following could be an empirical formula? A. C4H8 B. C2H6 C. CH D. C3H6 Explanation: CH could be an empirical formula. An empirical formula is the smallest expression of a chemical formula. To be empirical, a formula must be incapable of being reduced. For this reason, answer choices A, B, and D are incorrect, as they could all be reduced to a simpler form. Note that empirical formulas are not the same as compounds, which do not have to be irreducible. Two compounds can have the same empirical formula but different molecular formulas. The molecular formula is the actual number of atoms in the molecule. 6. What is the name for the reactant that is entirely consumed by the reaction? A. limiting reactant B. reducing agent C. reaction intermediate D. reagent Explanation: A limiting reactant is entirely used up by the chemical reaction. Limiting reactants control the extent of the reaction and determine the quantity of the product. A reducing agent is a substance that reduces the amount of another substance by losing electrons. A reagent is any substance used in a chemical reaction. Some of the most common reagents in the laboratory are sodium hydroxide and hydrochloric acid. The behavior and properties of these substances are known, so they can be effectively used to produce predictable reactions in an experiment. 7. What is the name for the horizontal rows of the periodic table? A. groups B. periods C. families D. sets Explanation: The horizontal rows of the periodic table are called periods. The vertical columns of the periodic table are known as groups or families. All of the elements in a group have similar properties. The relationships between the elements in each period are similar as you move from left to right. The periodic table was developed by Dmitri Mendeleev to organize the known elements according to their similarities. New elements can be added to the periodic table without necessitating a redesign. 8. What is the mass (in grams) of 7.35 mol water? A. 10.7 g B. 18 g C. 132 g D. 180.6 g Explanation: The mass of 7.35 mol water is 132 grams. You should be able to find the mass of various chemical compounds when you are given the number of mols. The information required to perform this function is included on the periodic table. To solve this problem, find the molecular mass of water by finding the respective weights of hydrogen and oxygen. Remember that water contains two hydrogen molecules and one oxygen molecule. The molecular mass of hydrogen is roughly 1, and the molecular mass of oxygen is roughly 16. A molecule of water, then, has approximately 18 grams of mass. Multiply this by 7.35 mol, and you will obtain the answer 132.3, which is closest to answer choice C. 9. Which of the following orbitals is the last to fill? A. 1s B. 3s C. 4p D. 6s Explanation: Of these orbitals, the last to fill is 6s. Orbitals fill in the following order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, and 7p. The number is the orbital number, and the letter is the sublevel identification. Sublevel s has one orbital and can hold a maximum of two electrons. Sublevel p has three orbitals and can hold a maximum of six electrons. Sublevel d has five orbitals and can hold a maximum of 10 electrons. Sublevel f has seven orbitals and can hold a maximum of 14 electrons. 10. What is the name of the binary molecular compound NO5? A. nitro pentoxide B. ammonium pentoxide C. nitrogen pentoxide D. pentnitrogen oxide Explanation: Nitrogen pentoxide is the name of the binary molecular compound NO5. The format given in answer choice C is appropriate when dealing with two nonmetals. A prefix is used to denote the number of atoms of each element. Note that when there are seven atoms of a given element, the prefix hepta- is used instead of the usual septa-. Also, when the first atom in this kind of binary molecular compound is single, it does not need to be given the prefix mono-. 11. What is the mass (in grams) of 1.0 mol oxygen gas? A. 12 g B. 16 g C. 28 g D. 32 g Explanation: The mass of 1.0 mol oxygen gas is 32 grams. The molar mass of oxygen can be obtained from the periodic table. In most versions of the table, the molar mass of the element is directly beneath the full name of the element. There is a little trick to this question. Oxygen is a diatomic molecule, which means that it always appears in pairs. In order to determine the mass in grams of 1.0 mol of oxygen gas, then, you must double the molar mass. The listed mass is 16, so the correct answer to the problem is 32. 12. Which kind of radiation has no charge? A. beta B. alpha C. delta D. gamma Explanation: Gamma radiation has no charge. This form of electromagnetic radiation can travel a long distance and can penetrate the human body. Sunlight and radio waves are both examples of gamma radiation. Alpha radiation has a 2+ charge. It only travels short distances and cannot penetrate clothing or skin. Radium and uranium both emit alpha radiation. Beta radiation has a 1– charge. It can travel several feet through the air and is capable of penetrating the skin. This kind of radiation can be damaging to health over a long period of exposure. There is no such thing as delta radiation. 13. What is the name of the state in which forward and reverse chemical reactions are occurring at the same rate? A. equilibrium B. constancy C. stability D. toxicity Explanation: When forward and reverse chemical reactions are taking place at the same rate, a chemical reaction has achieved equilibrium. This means that the respective concentrations of reactants and products do not change over time. In theory, a chemical reaction will remain in equilibrium indefinitely. One of the common tasks in the chemistry lab is to find the equilibrium constant (or set of relative concentrations that result in equilibrium) for a given reaction. In thermal equilibrium, there is no net heat exchange between a body and its surroundings. In dynamic equilibrium, any motion in one direction is offset by an equal motion in the other direction. 14. What is 119°K in degrees Celsius? A. 32°C B. –154°C C. 154°C D. –32°C Explanation: 119°K is equivalent to –154 degrees Celsius. It is likely that you will have to perform at least one temperature conversion on the HESI exam. To convert degrees Kelvin to degrees Celsius, simply subtract 273. To convert degrees Celsius to degrees Kelvin, simply add 273. To convert degrees Kelvin into degrees Fahrenheit, multiply by 9/5 and subtract 460. To convert degrees Fahrenheit to degrees Kelvin, add 460 and then multiply by 5/9. To convert degrees Celsius to degrees Fahrenheit, multiply by 9/5 and then add 32. To convert degrees Fahrenheit to degrees Celsius, subtract 32 and then multiply by 5/9. 15. What is the SI unit of energy? A. ohm B. joule C. henry D. newton Explanation: The joule is the SI unit of energy. Energy is the ability to do work or generate heat. In regard to electrical energy, a joule is the amount of electrical energy required to pass a current of one ampere through a resistance of one ohm for one second. In physical or mechanical terms, the joule is the amount of energy required for a force of one newton to act over a distance of one meter. The ohm is a unit of electrical resistance. The henry is a unit of inductance. The newton is a unit of force. 16. What is the name of the device that separates gaseous ions by their mass-to-charge ratio? A. mass spectrometer B. interferometer C. magnetometer D. capacitance meter Explanation: A mass spectrometer separates gaseous ions according to their mass-to-charge ratio. This machine is used to distinguish the various elements in a piece of matter. An interferometer measures the wavelength of light by comparing the interference phenomena of two waves: an experimental wave and a reference wave. A magnetometer measures the direction and magnitude of a magnetic field. Finally, a capacitance meter measures the capacitance of a capacitor. Some sophisticated capacitance meters may also measure inductance, leakage, and equivalent series resistance. 17. Which material has the smallest specific heat? A. water B. wood C. aluminum D. glass Explanation: Of the given materials, aluminum has the smallest specific heat. The specific heat of a substance is the amount of heat required to raise the temperature of one gram of the substance by one degree Celsius. In some cases, specific heat is expressed as a ratio of the heat required to raise the temperature of one gram of a substance by one degree Celsius to the heat required to raise the temperature of one gram of water by one degree Celsius. 18. What is the name for a reaction in which electrons are transferred from one atom to another? A. combustion reaction B. synthesis reaction C. redox reaction D. double-displacement reaction Explanation: In a redox reaction, also known as an oxidation-reduction reaction, electrons are transferred from one atom to another. A redox reaction changes the oxidation numbers of the atoms. In a combustion reaction, one material combines with an oxidizer to form a product and generate heat. In a synthesis reaction, multiple chemicals are combined to create a more complex product. In a double-displacement reaction, two chemical compounds trade bonds or ions and create two different compounds. Other common chemical reactions you may need to know for the HESI exam are the acid-base reaction, analysis reaction, single-displacement reaction, isomerization reaction, and hydrolysis reaction. 19. What are van der Waals forces? A. the weak forces of attraction between two molecules B. the strong forces of attraction between two molecules C. hydrogen bonds D. conjugal bonds Explanation: van der Waals forces are the weak forces of attraction between two molecules. The van der Waals force is considered to be any of the attractive or repulsive forces between electrons that are not related to electrostatic interaction or covalent bonds. Compared to other chemical bonds, the strength of van der Waals forces is small. However, these forces have a great effect on a substance’s solubility and other characteristics. The HESI exam may require you to demonstrate knowledge of all the major chemical forces. 20. Which of the following gases effuses the fastest? A. Cl2 B. O2 C. N2 D. H2