Chapter 6: Thermochemistry

Question 1

Energy

Answer 1

The capacity to do work or to produce heat

Question 2

Law of Conservation of Energy

Answer 2

Energy can be converted from one form to another but can be neither created nor destroyed (The energy gained by the surroundings must be equal to the energy lost by the system.)

Question 3

Potential energy

Answer 3

Energy due to position or composition

Question 4

Kinetic energy

Answer 4

Energy due to the motion of the object and depends on the mass of the object and its velocity (KE = 1/2 x m x v^2)

Question 5

Heat

Answer 5

The transfer of energy between two objects due to a temperature difference

Question 6

Work

Answer 6

Force acting over a distance

Question 7

Pathway

Answer 7

The specific conditions that determine how energy transfer is divided between work and heat

Question 8

State function (property)

Answer 8

A property that is independent of the pathway

e.g.: Energy change, internal energy, pressure, volume, enthalpy

Question 9

System

Answer 9

Part of the universe on which we wish to focus attention

Question 10

Surroundings

Answer 10

Everything else in the universe

Question 11

Exothermic

Answer 11

Energy flows out of the system

Question 12

Endothermic

Answer 12

Energy flows into the system

Question 13

Thermodynamics

Answer 13

The study of energy and its interconversions

Question 14

The First Law of Thermodynamics

Answer 14

The energy of the universe is constant

Question 15

Internal energy

Answer 15

The sum of the kinetic and potential energies of all the “particles” in the system

Question 16

Change in internal energy

Answer 16

∆E = q + w
E = internal energy
q = heat
w = work

Question 17

When q is positive…

Answer 17

A quantity of energy flows into the system via heat (an endothermic process)

Question 18

When q is negative…

Answer 18

A quantity of energy flows out of the system via heat (an exothermic process)

Question 19

When w is positive…

Answer 19

The surroundings do work on the system (energy flows into the system)

Question 20

When w is negative…

Answer 20

The system does work on the surroundings (energy flows out of the system)

Question 21

Work equation

Answer 21

Compression: Work = P x A x ∆h = P∆V
Expansion: Work = -P∆V

Question 22

Enthalpy

Answer 22

H = E + PV
H = enthalpy
E = internal energy of the system
P = pressure of the system
V = volume of the system

Question 23

At constant pressure (where only PV work is allowed)…

Answer 23

The change in enthalpy ∆H of the system is equal to the energy flow as heat q (Heat of reaction = change in enthalpy)

Question 24

Enthalpy change equation

Answer 24

∆H = Hproducts - Hreactants

Question 25

When ∆H is positive...

Answer 25

The products of a reaction have a greater enthalpy than the reactants, so heat will be absorbed by the system (ENDOTHERMIC)

Question 26

When ∆H is negative...

Answer 26

The reactants of a reaction have a greater enthalpy than the products, so heat will be generated by the system (EXOTHERMIC)

Question 27

Calorimeter

Answer 27

The device used experimentally to determine the heat associated with a chemical reaction

Question 28

Calorimetry

Answer 28

The science of measuring heat based on observing the temperature change when a body absorbs or discharges energy as heat

Question 29

Heat capacity

Answer 29

C = heat absorbed / increase in temperature

Question 30

Specific heat capacity

Answer 30

The energy required to raise the temperature of one gram of a substance by one degree Celsius

Question 31

Molar heat capacity

Answer 31

The energy required to raise the temperature of one mole of a substance by one degree Celsius

Question 32

Energy (as heat) equation

Answer 32

``` q = s x m x ∆T s = specific heat capacity m = mass of solution ∆T = increase in temperature ```

Question 33

Constant volume calorimetry equation

Answer 33

``` q = s x ∆T s = specific heat capacity of the calorimeter ```

Question 34

Hess's Law

Answer 34

In going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one step or in a series of steps

Question 35

Standard enthalpy of formation (∆H˚f)

Answer 35

The change in enthalpy that accompanies the formation of 1 mole of a compound from its elements with all substances in their standard states

Question 36

Law of Summation of Heats of Formation

Answer 36

∆H˚reaction = sum of the heats of formation for the products multiplied by their coefficients in a balanced chemical equation - sum of the heats of formation for the reactants multiplied by their coefficients in a balanced chemical equation

Question 37

Fossil fuels

Answer 37

Coal, petroleum, or natrual gas

Question 38

Petroleum

Answer 38

A thick, dark liquid composed mostly of compounds called hydrocarbons that contain carbon and hydrogen

Question 39

Natural gas

Answer 39

Usually associated with petroleum deposits, consists mostly of methane, but it also contains significant amounts of ethane, propane, and butane

Question 40

Coal

Answer 40

Formed from the remains of plants that were buried and subjected to high pressure and heat over long periods of time

Question 41

Greenhouse effect

Answer 41

A warming effect exerted by the earth's atmosphere (particularly CO2 and H2O) due to thermal energy retained by absorption of infrared radiation

Question 42

Syngas

Answer 42

Synthetic gas, a mixture of carbon monoxide and hydrogen, obtained by coal gasification