AFOQT Physical Science questions and answers.

Absolute zero the lowest possible temperature (-273.15 degrees Celsius) Atmospheric pressure The pressure exerted by the gases in the air. Units of measurement are kilopascals (kPa), atmospheres (atm), millimeters of mercury (mm Hg) and Torr. Standard atmospheric pressure is 100 kPa, 1 atm, 760 mm Hg or 760 Torr. Atom The smallest particle of an element; a nucleus and its surrounding electrons. Atomic mass The mass of an atom measured in atomic mass units (amu). An atomic mass unit is equal to one-twelfth of the atom of carbon-12. Atomic mass is now more generally used instead of atomic weight. Example: the atomic weight of cholrine is about 35 g/mol. Atomic number Also known as proton number, it is the number of electrons or the number of protons in an atom. Example: the atomic number of gold is 79 Atomic weight A common term used to mean the average molar mass of an element. This is the mass per mole of atoms. Example: the atomic weight of chlorine is about 35 g/mol. Boiling point the temperature at which a substance undergoes a phase change from a liquid to a gas Celsius scale a temperature scale on which the freezing point of water is at 0 degrees and the normal boiling point at standard atmospheric pressure is 100 degrees Change of state A change between two of the three states of matter, solid, liquid and gas. Example: when water evaporates it changes from a liquid to a gaseous state. Compound A chemical consisting of two or more elements chemically bonded together. Example: Calcium can combine with carbon and oxygen to make calcium carbonate (CaCO3), a compound of all three elements. Condensation The formation of a liquid from a gas. This is a change of state, also called a phase of change. Conduction (i) the exchange of heat (heat conduction) by contact with another object, or (ii) allowing the flow of electrons (electrical conduction). Convection The exchange of heat energy with the surroundings produced by the flow of a fluid due to being heated or cooled. Decay (radioactive decay) The way that a radioactive element changes into another element due to loss of mass through radiation. Example: uranium 238 decays with the loss of an alpha particle to form thorium 234. Density The mass per unit volume (e.g. g/cm3) Diffusion The slow mixing of one substance with another until the two substances are evenly mixed. Mixing occurs because of differences in concentration with the mixture. Diffusion works rapidly with gases, very slowly with liquids. Dissolve to break down a substance in a solution without causing a reaction Electrical potential the energy produced by an electrochemical cell and measured by the voltage or electromotive force (emf) Electron A tiny, negatively charged particle that is part of an atom. The flow of electrons through a solid material such as a wire produces an electric current. Element A substance that cannot be decomposed into simpler substance by chemical means. Examples: calcium, iron, gold. Explosive A substance which, when a shock is applied to it, decomposes very rapidly, releasing a very large amount of heat and creating a large volume of gases as a shock wave. Fluid Able to flow; either a liquid or a gas. Freezing point The temperature at which a substance undergoes a phase change from a liquid to a solid. It is the same temperature as the melting point. Gamma rays Waves of radiation produced as the nucleus of a radioactive element rearranges itself into a tighter cluster of protons and neutrons. Gamma rays carry enough energy to damage living cells. Gas/gaseous phase A form of matter in which the molecules form no definite shape and are free to move about to uniformly fill any vessel they are put in. A gas can easily be compressed into a much smaller volume. Group A vertical column in the Periodic Table. There are eight groups in the table. Their numbers correspond to the number of electrons in the outer shell of the atoms in the group. Example: Group 2 contains beryllium, magnesium, calcium, strontium, barium and radium. Half-life the time it takes for the radiation coming from a sample of a radioactive element to decrease by half Heat the energy that is transferred when a substance is at a different temperature to that of its surroundings Heat capacity The ratio of the heat supplied to a substance, compared with the rise in temperature that is produced. Heat of combustion The amount of heat given off by a mole of substance during combustion. This heat is a property of the substance and is the same no matter what kind of combustion is involved. Example: heat of combustion of carbon is 94.05 kcal (x4.18 kJ/kcal=393.1 kJ) Ion An atom, or group of atoms, that has gained or lost one or more electrons and so developed an electrical charge. Ions behave differently from electrically neutral atoms and molecules. They can move in an electric field, and they can also bind strongly to solvent molecules such as water. Positively charged ions are called cations; negatively charged ions are called anions. Ions can carry an electrical current through solutions. Isotope One of two or more atoms of the same element that have the same number of protons in their nucleus (atomic number), but which have a different number of neutrons (atomic mass). Example; carbon-12 and carbon-14. Kinetic energy The energy an object has by virtue of its being in motion. Latent heat The amount of heat that is absorbed or released during the process of changing state between gas, liquid or solid. For example, heat is absorbed when a substance melts and it is released again when the substance solidifies. Liquid/liquid phase a form of matter that has a fixed volume but not fixed shape