Chapter 6 Thermochemistry

Question 1

What is energy?

Answer 1

the potential or capacity to move matter.

Question 2

Kinetic energy. Ek = 1/2mv^2

where m = mass and v = velocity

Answer 2

the energy associated with an object by virtue of its motion. An object of mass and speed or velocity has kinetic energy.

Question 3

Potential energy. Ep = mgh

where m = mass, g = is the constant acceleration of gravity(9.807m/s^2), and h = height.

Answer 3

is the energy an object has by virtue of its position in a field of force.

Question 4

Internal energy. Etot = Ek + Ep + U.

where Ek= kinetic energy, Ep = Potential energy and U = internal energy

Answer 4

is the sum of the kinetic and potential energies of the particles making up a substance.

Question 5

Calorie (cal).

Answer 5

is the common unit of energy. It is defined as the amount of energy required to raise the temperature of one gram of water by one degree Celsius. So,
1 cal = 4.184J

Question 6

Law of Conservation of Energy

Answer 6

energy may be converted from one form to another, but the total quantity of energy remains constant.

Question 7

Work, w.
Positive (+) when work is done on a system.
Negative (-) when the system does work on the surroundings.

Answer 7

is an energy transfer (or energy flow) into or out of a thermodynamic system whose effect on the surroundings is equivalent to moving an object through a field of force.

Question 8

Heat, q.
Positive (+) when a system absorbs heat.
Negative (-) when a system evolves (loses) heat.

Answer 8

is an energy transfer (energy flow) into or out of a thermodynamic system that results from a temperature difference between the system and its surroundings.

Question 9

The change in internal energy of a system.

Answer 9

is Uf-Ui, the change in internal energy is Ufinal - Uinitial.

Question 10

First Law of Thermodynamics

Answer 10

states that the change in internal energy of a system

Question 11

Heat of Reaction

Answer 11

(at a given temperature) is the heat, q, absorbed or evolved from a reaction system to retain a fixed temperature of the system under the conditions specified for the reaction. note: chemical reactions or physical changes are specified depending on the sign of q.

Question 12

Exothermic Process

Answer 12

is a chemical reaction or a physical change in which heat is evolved (q is negative, energy subtracted).

Question 13

Endothermic Process

Answer 13

is a chemical reaction or a physical change in which heat is absorbed (q is positive, energy added).

Question 14

Pressure-Volume Work

w = -P

Answer 14

w, equals the negative of the pressure times the change in volume of the system.
note: w, is defined from the perspective of the system, when

Question 15

Enthalpy, H.
H = U + PV,
where U is internal energy, P is pressure and V is volume.

Answer 15

is a state function; at constant pressure, the enthalpy change is equal to the heat absorbed or released; enthalpy is an extensive property; the SI unit of enthalpy is Joule (J).

Question 16

Heat of Reaction, q.

Answer 16

q =

Question 17

Enthalpy of Reaction a.k.a Enthalpy Change for the Reaction.

Answer 17

the change in enthalpy,

Question 18

How are the terms enthalpy of reaction and heat of reaction are related?

Answer 18

the change in enthalpy of the system is the heat absorbed or released by a system undergoing a physical or chemical change at constant pressure.

Question 19

Thermochemical Equations
note:
⇾remember to multiply the value of

Answer 19

is the chemical equation for a reaction (including phase labels) in which the equation is given a molar interpretation, and the enthalpy of reaction for these molar amounts is written directly after the equation.

Question 20

Heat Capacity, C

q = C

Answer 20

of a sample of substance is the quantity of heat needed to raise the temperature of the sample of substance one degree Celsius (or one Kelvin). Heat capacities are directly proportional to the amount of substance and are listed for molar amounts.

Question 21

Specific Heat

q = s × m ×

Answer 21

is the quantity of heat required to raise the temperature of one gram of a substance by one degree Celsisu (or one Kelvin) at constant pressure.

Question 22

Hess’s Law of Heat Summation

Answer 22

states that for a chemical equation that can be written as the sum of two or more steps, the enthalpy change for the overall equation equals the sum of the enthalpy changes for the individual steps.

Question 23

Standard Enthalpy of Formation a.k.a Standard Heat of Formation

Answer 23

of a substance, is the enthalpy change for the formation of one mole of the substance in its standard state from its elements in their reference form and in their standard states.

Question 24

Reference Form

Answer 24

an element for the purpose of specifying the formation reaction is usually the stablest form (physical state and allotrope) of the element under standard thermodynamic conditions.