Energetics

Question 1

what is an enthalpy change?

Answer 1

a change in heat measured at constant pressure

Question 2

is bond making an exothermic or endothermic process?

Answer 2

exothermic

Question 3

is bond breaking an exothermic or endothermic process?

Answer 3

endothermic

Question 4

what is the formula for enthalpy change?

Answer 4

enthalpy change of products- enthalpy change of reactants

Question 5

what does bond energy represent?

Answer 5

• the quantity of energy evolved when the bond is formed

- the amount of energy absorbed when the bond is broken

Question 6

what is said about bonds that have very high bond energies?

Answer 6

they are unreacitve

Question 7

standard molar enthalpy change of formation?

Answer 7

the enthalpy change for the formation of one mole of a compound from its elements under standard conditions

Question 8

standard molar enthalpy change of combustion?

Answer 8

the enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions

Question 9

standard molar enthalpy change of atomization

Answer 9

the enthalpy change when one mole of a substance decomposes completely into gaseous atoms under standard conditions

Question 10

standard molar enthalpy change of neutralization

Answer 10

the enthalpy change when one mole of acid reacts with one mole of base to form one mole of water under standard conditions

Question 11

first ionization energy

Answer 11

energy required to convert one mole of gaseous atom into one mole of singly positively charged ions

Question 12

first electron affinity

Answer 12

the enthalpy change when one mole of gaseous atoms is converted into one mole of singly negatively charged ions

Question 13

lattice energy (LE)

Answer 13

the enthalpy change when one mole of an ionic compound is formed from its gaseous ions

Question 14

the enthalpy change of solution

Answer 14

the enthalpy change when one mole of solute dissolves to form an infinitely dilute solution under standard conditions.

Question 15

hydration enthalpy

Answer 15

the enthalpy change when one mole of gaseous ions is completely solvated by water molecules.

Question 16

what do arrowheads represent in a born-haber cycle?

Answer 16

upward arrow(↑)- positive enthalpy change
downward arrow(↓)- negative enthalpy change

Question 17

for cations, what is the relationship between ionic radius and lattice energy?

Answer 17

for cations, the smaller the ionic radius, the higher the lattice energy

Question 18

for anions, what is the relationship between ionic radius and lattice energy?

Answer 18

for anions, the larger the ionic radius, the higher the lattice energy

Question 19

state Hess’ Law of Constant Heat Summation

Answer 19

Hess’ Law of Constant Heat Summation states that the energy change in converting reactants A and B to products X and Y is the same, regardless of the path taken, provided the initial and final conditions remain the same

Question 20

how can enthalpy changes be determined? (2)

Answer 20

1) thermo chemical cycles

2) born-haber cycles

Question 21

define the term bond energy

Answer 21

this is the energy required to break the covalent bonds in one mole of a gaseous substance