CHEM 115 TEST PAPER 2026/2027 QUESTIONS AND
SOLUTIONS RATED A+
✔✔Gamma emission - ✔✔a type of radioactive decay in which gamma rays are emitted
from an excited nucleus.
✔✔How does alpha decay affect mass number (A) and atomic number (Z)? -
✔✔decreases A by 4 and Z by 2.
✔✔How does beta decay affect mass number (A) and atomic number (Z)? -
✔✔increases Z by 1 and A remains unchanged.
✔✔How does positron emission affect mass number (A) and atomic number (Z)? -
✔✔decreases Z by 1 and A remains unchanged.
✔✔How does electron capture affect mass number (A) and atomic number (Z)? -
✔✔decreases Z by 1 and A remains unchanged.
✔✔How does gamma emission affect mass number (A) and atomic number (Z)? - ✔✔A
and Z remain unchanged.
✔✔How do you predict the mode of radioactive decay? - ✔✔1. neutron rich nuclides -
undergo B- decay, 2. proton-rich nuclides - undergo B+ emission and/or electron
capture, 3. heavy nuclides - alpha decay.
✔✔kinetic energy - ✔✔the energy of motion
✔✔potential energy - ✔✔the stored energy
✔✔internal energy of a system - ✔✔the sum of all potential and kinetic energy
components
✔✔reactants, products - ✔✔internal energy changes when _______ change to
_________
✔✔exothermic - ✔✔energy released to the surroundings; bonds forming; E initial > E
final
✔✔endothermic - ✔✔energy absorbed from surroundings; bonds broken; E final > E
initial
✔✔work - ✔✔the energy transferred when an object is moved against a force
, ✔✔heat - ✔✔the energy transferred from hotter object to colder one
✔✔first law of thermodynamics - ✔✔total energy of a system plus surroundings remains
constant
✔✔Change in Energy - ✔✔∆E=q+w
✔✔enthalpy (H) - ✔✔E+PV
✔✔Hess's Law - ✔✔the enthalpy change of an overall process is the sum of the
enthalpy changes of its individual steos
✔✔soluble - ✔✔when a solid dissolves in a solvent
✔✔less - ✔✔gases tend to become ______ soluble as temperature increases
✔✔more - ✔✔solids tend to become _______ soluble as temperature increases
✔✔increases, increases - ✔✔ionization energy ________ as it goes down and
_________ as it goes across
✔✔increases, decreases - ✔✔atomic radius ________ as it goes down and _________
as it goes across
✔✔electron affinity - ✔✔how likely an element is to gain an electron
✔✔decreases, increases - ✔✔electronegativity _________ as it goes down and
____________ as it goes across
✔✔dipole-dipole forces - ✔✔important for polar molecules in a condensed phase.
stabilizing
✔✔stabilizing forces - ✔✔lower the energy of the system
✔✔higher boiling point - ✔✔stronger intermolecular interactions, greater size/mass
✔✔hydrogen bond - ✔✔one molecule has an H-X covalent bond (X = N, O, or F) and
another molecule has a lone pair
✔✔polarizability - ✔✔how easily the electron cloud can be distorted. increases down a
group (with size) and decreases across a period (as effective nuclear charge, Zeff,
increases). Cations are less polarizable than parent ions, anions are more polarizable
than parent ions.
SOLUTIONS RATED A+
✔✔Gamma emission - ✔✔a type of radioactive decay in which gamma rays are emitted
from an excited nucleus.
✔✔How does alpha decay affect mass number (A) and atomic number (Z)? -
✔✔decreases A by 4 and Z by 2.
✔✔How does beta decay affect mass number (A) and atomic number (Z)? -
✔✔increases Z by 1 and A remains unchanged.
✔✔How does positron emission affect mass number (A) and atomic number (Z)? -
✔✔decreases Z by 1 and A remains unchanged.
✔✔How does electron capture affect mass number (A) and atomic number (Z)? -
✔✔decreases Z by 1 and A remains unchanged.
✔✔How does gamma emission affect mass number (A) and atomic number (Z)? - ✔✔A
and Z remain unchanged.
✔✔How do you predict the mode of radioactive decay? - ✔✔1. neutron rich nuclides -
undergo B- decay, 2. proton-rich nuclides - undergo B+ emission and/or electron
capture, 3. heavy nuclides - alpha decay.
✔✔kinetic energy - ✔✔the energy of motion
✔✔potential energy - ✔✔the stored energy
✔✔internal energy of a system - ✔✔the sum of all potential and kinetic energy
components
✔✔reactants, products - ✔✔internal energy changes when _______ change to
_________
✔✔exothermic - ✔✔energy released to the surroundings; bonds forming; E initial > E
final
✔✔endothermic - ✔✔energy absorbed from surroundings; bonds broken; E final > E
initial
✔✔work - ✔✔the energy transferred when an object is moved against a force
, ✔✔heat - ✔✔the energy transferred from hotter object to colder one
✔✔first law of thermodynamics - ✔✔total energy of a system plus surroundings remains
constant
✔✔Change in Energy - ✔✔∆E=q+w
✔✔enthalpy (H) - ✔✔E+PV
✔✔Hess's Law - ✔✔the enthalpy change of an overall process is the sum of the
enthalpy changes of its individual steos
✔✔soluble - ✔✔when a solid dissolves in a solvent
✔✔less - ✔✔gases tend to become ______ soluble as temperature increases
✔✔more - ✔✔solids tend to become _______ soluble as temperature increases
✔✔increases, increases - ✔✔ionization energy ________ as it goes down and
_________ as it goes across
✔✔increases, decreases - ✔✔atomic radius ________ as it goes down and _________
as it goes across
✔✔electron affinity - ✔✔how likely an element is to gain an electron
✔✔decreases, increases - ✔✔electronegativity _________ as it goes down and
____________ as it goes across
✔✔dipole-dipole forces - ✔✔important for polar molecules in a condensed phase.
stabilizing
✔✔stabilizing forces - ✔✔lower the energy of the system
✔✔higher boiling point - ✔✔stronger intermolecular interactions, greater size/mass
✔✔hydrogen bond - ✔✔one molecule has an H-X covalent bond (X = N, O, or F) and
another molecule has a lone pair
✔✔polarizability - ✔✔how easily the electron cloud can be distorted. increases down a
group (with size) and decreases across a period (as effective nuclear charge, Zeff,
increases). Cations are less polarizable than parent ions, anions are more polarizable
than parent ions.
