Thermodynamics

Question 1

Define heat.

Answer 1

Transfer of thermal energy from a hotter object to a colder object

Question 2

What is 0˚ C in Kelvin?

Answer 2

273K

Question 3

Conversion of F –> C

Answer 3

(9/5)C + 32

Question 4

When solids or liquids experience a change in temperature, their length or volume changes. What are the corresponding formulas to determine this change?

Answer 4

For ∆L (applicable to solids only):
∆L = αL∆T
For ∆V (solids & liquids):
∆V = βV∆T

**α and β are constant values

Question 5

State functions

Answer 5

Functions that describe the equilibrium state of a system, independent of the path taken by the system to arrive to its present state
Pressure, volume, temperature, entropy

Question 6

Process/path functions

Answer 6

Functions that describe the path taken by a system to transition from 1 equilibrium state to another
Work, heat

Question 7

Equation to calculate total internal energy of a system:

Answer 7

∆U = Q - W

Question 8

If W is negative, work is being done (on/by) the system.
If W is positive, work is being done (on/by) the system.

Answer 8

-W = work is done on the system
+W = work is done by the system

Question 9

3 methods of heat transfer:

Answer 9

Conduction, convection, radiation

Question 10

Conduction

Answer 10

direct transfer of energy through physical contact/molecular collisions

Question 11

Convection

Answer 11

transfer of heat by the physical motion of a liquid or gas over a material
*SOLIDS don’t participate in convection

Question 12

Radiation

Answer 12

transfer of energy by electromagnetic waves ;can transfer energy through a vacuum
Ex: Sun warming the Earth

Question 13

During a phase change, temperature is (changing/constant), even though heat is added or removed.

Answer 13

Constant

Question 14

SI unit of heat

Answer 14

Joules (J)

Question 15

Specific heat of water

Answer 15

1 cal/g˚C or 4.184 J/g*K or 420 J/˚C

Question 16

0th Law of Thermodynamics

Answer 16

Objects that are in thermal contact & not in thermal equilibrium, will exchange heat traveling from the hotter object to the cooler object

Question 17

1st Law of Thermodynamics

Answer 17

Energy can be transferred, but it isn’t created or destroyed.

Question 18

2nd Law of Thermodynamics

Answer 18

Entropy of an isolated system always increases; heat will flow from a hotter object to a colder object

Question 19

Calculating heat energy (q)

Answer 19

q = mC∆T
c is the specific heat capacity

Question 20

Difference between specific heat capacity and heat capacity

Answer 20

Specific heat capacity - amt. of heat required to raise the temp of 1 g of substance by 1˚C
Heat capacity - amt. of heat required to raise temp of entire sample by 1˚C

Question 21

Another version of calculating heat:

Answer 21

q = C∆T
no mass required
*If given a problem where one material loses heat & other gains heat, set q’s equal to each other

Question 22

Change in entropy equation

Answer 22

∆S = Qrev/T
Qrev is the heat gained or lost in a reversible process
T is measured in Kelvin

Question 23

True or false:
In order to concentrate or confine energy, it requires work.

Answer 23

Yes, because energy spontaneously disperses, so in order for it to be confined some amount of work should be used to confine it to one area.

Question 24

Calorimeters are an example of what type of system: isolated, closed or open?

Answer 24

Isolated systems because neither energy nor matter is exchanged.

Question 25

2 main equations to know for calorimeters

Answer 25

1. Heat absorbed by calorimeter: Qcalorimeter = Ccalorimeter*∆T
2. Qwater/sample = Cmass∆T

Question 26

The temperature of a system is also a measure of what?

Answer 26

The average kinetic energy of the molecules in that system.

Question 27

Calculating ∆Eth (change in thermal energy)

Answer 27

∆Eth = (3/2)nR∆T
n is # of moles
R is 8.314
∆T is in K

Question 28

How does thermal energy change in an isothermal process?

Answer 28

Isothermal - stays the same

Question 29

When a gas expands, what is true about work?

Answer 29

The work done by the gas is positive.

Question 30

When a gas is compressed, what is true about work?

Answer 30

The work done by the gas is negative.

Question 31

W on the gas = - Work by the gas

Question 32

In a PV graph, if volume stays the same, what is true about work? What if the volume increases?

Answer 32

Work = 0; Work increases

Question 33

When looking at a PV diagram, how do you calculate work?

Answer 33

Take the area under the curve. Remember the work you calculate is “the work done BY the gas”. To get work done on the gas, take the opposite sign of the same value.

Question 34

Define the following processes:
Isobaric
Isochoric
Isothermal
Adiabatic

Answer 34

Isobaric - constant pressure
Isochoric - constant volume
Isothermal - constant temperature
Adiabatic - ideal gas is compressed very quickly, no heat exchange occurs between the system & the environment

Question 35

How do you achieve the following processes?

Answer 35

Isobaric - insuring the piston can move up or down without friction
Isochoric - locking a piston in place
Isothermal - carrying out the process slowly in a cylinder that is in good thermal contact w/ surrounding
Adiabatic - carrying out the process rapidly in a well-insulated cylinder

Question 36

In an isobaric process, how is the volume affected if the temperature of the process is increased?

Answer 36

Volume increases as temperature increases.

Question 37

Compare a closed vs. isolated system.

Answer 37

Closed - heat can be exchanged w/ the surroundings, but mass can not be; bomb cell
Isolated - neither heat nor mass can be exchanged w/ the surroundings; calorimeter device

Question 38

Comparing adiabatic vs. isothermal graph

Answer 38

Question 39

What is the equation to calculate (energy released/absorbed) during a phase change when temperature is constant.

Answer 39

q = m*L
L is the latent heat of vaporization or latent heat of fusion (usually given in the question)
UNITs are kj/mol or cal/gram