Chapter 5 - Thermochemistry

Question 1

what is a system?

Answer 1

the part of the universe chosen for study

Question 2

what are surroundings?

Answer 2

the part of the universe outside the system in which these interactions can be detected

Question 3

what is work (w)?

Answer 3

work is done hen a force acts through a distance,
w = -Pext * ΔV
w = F*d

Question 4

what is heat (q)?

Answer 4

energy transferred between a system and its surroundings as a result of a temperature difference, q = mcΔT

Question 5

what is specific heat (c)?

Answer 5

quantity of heat required to change the temperature of a system by one degree for one gram of the substance (J/g*C)

Question 6

what is an endothermic reaction?

Answer 6

the corresponding situation is a temperature decrease in an isolated system or a gain of heat from the surroundings by a non-isolated system

Question 7

what is an exothermic reaction?

Answer 7

one that produces a temperature increase in an isolated system or, in a non-isolated system, gives off heat to the surroundings

Question 8

what is a calorimeter?

Answer 8

a device for measuring quantities of heat

Question 9

what is the 1st Law of Thermodynamics?

Answer 9

A system contains ONLY internal energy, ΔU = q + w; the energy of an isolated system is constant

• heat is absorbed by the system, q>0; work is done on the system, w>0
• heat is given off by the system, q

Question 10

what is a state function?

Answer 10

any property that has a unique value for a specific state of system

Question 11

what is enthalpy (H)?

Answer 11

the sum of the internal energy and the pressure-volume product of a system

H = U + PV, ΔH = ΔU + PΔV, ΔH =q(p)

Question 12

what is standard enthalpy of formation?

Answer 12

pure elements in reference from is 0; the enthalpy change for the overall reaction is the sum of the standard enthalpy changes of the individual steps
ΔHf = ΣProducts - ΣReactants

Question 13

what is molar heat capacity?

Answer 13

is the amount of heat needed to raise the temperature of 1mol of the substance by 1 Kelvin (1K), Using C all four factors can be expressed in one equation that describes the temperature change resulting from a heat transfer

q = nCΔT

Question 14

what is expansion work?

Answer 14

A gas in a container with movable walls can be expanded, and this expansion results in a movement AGAINST THE FORCE EXERTED BY THE WALLS. Thus, work is done in moving the walls of the container

wsys = -Pext*ΔV
wsys = -wsurr

Question 15

what is the Zeroth Law of Thermodynamics?

Answer 15

if two systems, A and B are separately in thermal equilibrium with a third system, C, then they are in thermal equilibrium with each other

Question 16

How are the system and surroundings related, via Law of thermodynamics?

Answer 16

Whatever the system loses, the surroundings gains, and vice versa

qsys = -qsurr
wsys = -wsurr

Question 17

what is heat measurement: calorimetry?

Answer 17

Isolated systems

ΔEsys = qsys + wsys

Question 18

what is a bomb calorimeter?

Answer 18

a bomb calorimeter is to measure the heat evolved in a combustion reaction.
chemical energy is converted to thermal energy, and the temperature of the system rises

qrnx = -qcalorimeter (Where qcalorimeter = qbomb + qwater +…)

qcalorimeter = c*ΔT

Question 19

what are thermochemical equations?

Answer 19

a chemical equation that shows the enthalpy relation between products and reactants
magnitude of enthalpy is directly proportional to the amount of reactant consumed

ΔHrxn = ΣVpProducts - ΣVrReactants

Question 20

what is heat of fusion?

Answer 20

the heat absorbed when a solid melts (s -> l)

Question 21

what is heat of vaporization?

Answer 21

heat is absorbed when a liquid vaporizes (l -> g)

Question 22

what is an extensive property?

Answer 22

depends on the amount of material (eg. ΔH)

Question 23

what is an intensive property?

Answer 23

doesn’t depend on the amount of material

Question 24

what is a path function?

Answer 24

depend on the sequences of the steps that the system takes from the initial to the final state;

• heat
• distance
• and work

Question 25

What is Hess’s Law?

Answer 25

If a reaction proceeds in steps, the overall change in ΔH is the algebraic sum of the ΔH’s of the individual steps

Question 26

One-step vs. two-step gas expansion?

Answer 26

• ΔU is the same for the single and two stage expansion process because internal energy is a state function
• However, more work is done in the two-stage expansion because work is path function

Question 27

what is a state function?

Answer 27

depends only on the initial and final state of the system;
ΔH
ΔS
ΔG
ΔP
ΔU
ΔT