Thermochemistry

Question 1

What is thermochemistry?

Answer 1

Thermochemistry is the science concerned with the amount of heat released or absorbed during chemical and physical changes.

Question 2

What is energy?

Answer 2

Energy is the capacity to supply heat or do work.

Question 3

What is potential energy?

Answer 3

Potential energy is the energy an object has because of its relative position, composition, or condition.

Question 4

What is kinetic energy?

Answer 4

Kinetic energy is the energy an object possesses because of its motion.

Question 5

What is thermal energy?

Answer 5

Thermal energy is kinetic energy associated with the random motion of atoms and molecules.

Question 6

What is heat?

Answer 6

Heat is the transfer of energy between two bodies at different temperatures.

Question 7

What is an exothermic process?

Answer 7

An exothermic process is a change that releases heat.

Question 8

What is an endothermic process?

Answer 8

An endothermic process is a reaction or change that absorbs heat.

Question 9

What is a calorie?

Answer 9

A calorie is the amount of energy reqired to raise 1 gram of water 1 degree Celsius.

Question 10

What is a joule?

Answer 10

A joule is the amount of energy used when a force of 1 newton moves an object 1 meter.

Question 11

What is the relationship between calories and joules?

Answer 11

1 calorie = 4.184 joules

Question 12

What is heat capacity?

Answer 12

The heat capacity (C) of a body of matter is the quantity of heat (q) it absorbs or releases when it experiences a temperature change (ΔT) of 1 degree Celsius.

C = q / ΔT

Question 13

What is specific heat capacity?

Answer 13

The specific heat (c) of a substance is the quantity of heat required to raise the temperature of 1 gram of a substance 1 degree Celsius.

c = q / mΔT

Question 14

What is internal energy?

Answer 14

Internal energy (U) is the total of all possible kinds of energy present in a substance.

Question 15

What is the relationship between internal energy, heat, and work?

Answer 15

ΔU = q + w

Question 16

What is expansion work?

Answer 16

Expansion work occurs when a system pushes back the surroundings against a restraining pressure, or when the surroundings compress the system.

Question 17

What is a state function?

Answer 17

A state function is a property depending only on the state of the system, and not the path taken to reach that state.

Question 18

What is enthalpy?

Answer 18

Enthalpy (H) is defined as the sum of a system’s internal energy (U) and the mathematical product of its pressure (P) and volume (V).

H = U + PV

Question 19

What is the formula for enthalpy change at a constant pressure?

Answer 19

ΔH = ΔU + PΔV = q_p, where q_p is the heat of reaction at a constant pressure.

Question 20

What is standard enthalpy of combustion?

Answer 20

Standard enthalpy of combustion (ΔH°_C) is the enthalpy change when one mole of a substance burns (combines vigorously with oxygen) under standard conditions (25ºC and 1 atm).

Question 21

What is standard enthalpy of formation?

Answer 21

Standard enthalpy of formation (ΔHº_f) is an enthalpy change for a reaction in which 1 mole of a pure substance is formed from free elements in their most stable states under standard conditions.

Question 22

What is Hess’s law?

Answer 22

Hess’s law states that if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps.

Question 23

What is the formula for determining the enthalpy change of a reaction if the corresponding enthalpies of formation of the reactants and the products are available?

Answer 23

ΔH_reaction = Σn • ΔHº_f (products) – Σn • ΔHº_f (reactants)