Chapter 5: Thermochemistry

Question 1

internal energy (E)

Answer 1

sum of heat added/released from a system
(sum of all kinetic and potential energies in the system)
ΔE= q+w
ΔE= Efinal-Einitial

Question 2

q (+)

Answer 2

head is transferred TO system FROM surroundings

-endothermic

Question 3

q (-)

Answer 3

heat leaves system

-exothermic

Question 4

w (+)

Answer 4

work is done ON system BY surroundings

Question 5

w (-)

Answer 5

work is done ON surroundings BY system

Question 6

enthalpy (H)

Answer 6

-flow of heat into/out of system under CONSTANT PRESSURE
H= E+PV
ΔH=ΔE+PΔV
ΔHrxn= Hproducts-Hreactants

Question 7

-ΔH

Answer 7

exothermic

Question 8

+ΔH

Answer 8

endothermic

Question 9

+ΔE

Answer 9

net GAIN of energy by system

Question 10

-ΔE

Answer 10

net LOSS of energy by system

Question 11

When HEAT is added to a system, internal energy ____. ______.

Answer 11

increases

Question 12

When volume increases, work is ___.

Answer 12

negative

Question 13

When volume decreases, work is ___.

Answer 13

positive

Question 14

q soln

Answer 14

• heat gained/lost by solution

- ΔT increase- exothermic (q rxn0)

Question 15

enthalpy of formation

Answer 15

• the enthalpy change for the formation of a compound from its constituent elements
• ∆Hf
• f means substance is formed from its constituent elements

Question 16

standard enthalpy change

Answer 16

• the enthalpy change when all the reactants and products are in their standard states
• ∆Hº
• º means standard-state conditions

Question 17

standard state (of a substance)

Answer 17

Its pure form at 1 atm and 298 K/25 degrees celsius

Question 18

standard enthalpy (heat) of formation

Answer 18

• change in enthalpy for the reaction that forms one mole of the compound from its elements
• all substances are in their standard states
• ∆Hºf

Question 19

kinetic energy

Answer 19

the energy of motion

Question 20

potential energy

Answer 20

energy stored by its position relative to other objects

Question 21

force

Answer 21

any push or pull exerted on an object

Question 22

heat

Answer 22

the energy transferred from a hotter object to a colder one

Question 23

first law of thermodynamics

Answer 23

1) Energy is conserved

Question 24

state function

Answer 24

function whose value depends ONLY on the present state of the system

Question 25

non-state function

Answer 25

function whose value depends on the path the system took to reach the present state

Question 26

pressure-volume work

Answer 26

The work involved in the expansion or compression of gases

Question 27

The change in enthalpy (∆H) ALSO equals ____

Answer 27

• qp

- the heat qp gained or lost at constant pressure

Question 28

State functions (examples)

Answer 28

1) enthalpy (H)
2) internal energy (E)
3) pressure
4) volume

Question 29

Non-state functions examples)

Answer 29

-qp

Question 30

enthalpy of reaction

Answer 30

• the enthalpy change that accompanies a reaction
• ∆Hrxn or ∆H
• also called ‘heat of reaction’

Question 31

calorimetery

Answer 31

the measurement of heat flow

Question 32

heat capacity

Answer 32

• The amount of heat required to raise its temperature by 1 K/1 °C
• determines the temperature change when an object absorbs a certain amount of heat
• C

Question 33

molar heat capacity

Answer 33

heat capacity of one mole of substance (Cm)

Question 34

specific heat capacity/ specific heat

Answer 34

heat capacity of one gram of a substance (Cs)

Question 35

bomb calorimeter

Answer 35

studies combustion reactions

• Substance is placed in a small cup inside insulated vessel called ‘bomb’
• Heat released when combustion occurs is absorbed by water and other components of calorimeter, causing water temperature to rise
• Will measure change in water temp.

Question 36

Hess’s law

Answer 36

If reaction is carried out in a series of steps, ∆H is the sum of the enthalpy changes of individual steps. (because enthalpy is state function)