B. First Law of Thermodynamics

Question 1

Define work and energy

Answer 1

1. Work - done when a body is moved against an opposing force
   w = Fd
   w = mgh (mechanical work)
2. Energy - ability to do work
   Ek = 1/2 mv^2
   Ep = mgh (gravitational)
   Ep = q1q2/4πεr (Coulomb)

Question 2

Differentiate open, closed, and isolated system

Answer 2

1. Open system - exchange energy and matter with surroundings
2. Closed system - exchange energy but not matter with its surroundings
3. Isolated system - exchange neither matter nor energy with surroundings

Question 3

Sign convention of work tarnsfer

Answer 3

Work done BY the system: (-) w
Work done ON the system: (+) w

Question 4

Work is the mode of transfer of energy that achieves or utilizes ____ motion in the surroundings

Heat is the mode of transfer of energy that achieves or utilizes _____ in the surroundings

Answer 4

work = uniform motion
heat = random atomic or molecular motion

Question 5

Type of work done when a system expands against an opposing force; give the formula

Answer 5

expansion work

w = - (p external) ΔV
dw = - (p external) dV

Question 6

When the external pressure is zero, the system does ____ work because ____

Answer 6

When the external pressure is zero, the system does no work because it has nothing to push against.

NOTE: Expansion against zero external pressure is called free expansion.

Question 7

Maximum expansion work is done when _____

Answer 7

a system remains in mechanical equilibrium (p ex = p) with its surroundings at all stages of expansion

→ the external pressure is only infinitesimally less than the pressure of the gas in the system

Question 8

What is a reversible process?

Answer 8

a process that can be reversed by an infinitesimal change in a variable

→ when a system is in a state of mechanical equilibrium, an infinitesimal change in the pressure results in opposite directions of motion.

Question 9

Work of isothermal, reversible expansion of a perfect gas from initial volume to final

Answer 9

w = -nRT ln (Vf/Vi)

Question 10

In an expansion, Vf is ___ than Vi and the sign of w is ___ because _____

Answer 10

In an expansion, Vf is greater than Vi and the sign of w is negative because energy leaves the system as the system does expansion work

Question 11

For a given change in volume, more work is done the ____ the temperature of the confined gas

Answer 11

higher

w = -nRT ln (Vf/Vi)
↑w = ↑T = ↑P of gas = ↑P external

Question 12

Define heat/heating

Answer 12

transfer of energy in the form of heat when there is a difference in temperature either by conduction or radiation

Question 13

Differentiate diathermic and adiabatic walls

Answer 13

1. Diathermic - permits transfer of energy in the form of heat from hot to cold
2. Adiabatic - do not permit heat transfer

Question 14

Endothermic vs exothermic process

Answer 14

1. Endothermic - diathermic container absorbs energy as heat from surroundings
2. Exothermic - diathermic container releases energy as heat to surroundings

Question 15

simple way of measuring the heat absorbed or released by a system

Answer 15

q = CΔT

Question 16

Why specific heat capacity or molar heat capacity is used in calculations instead of heat capacity only?

Answer 16

heat capacity is an extensive property (changes depending on the amount of substance)

Question 17

Compare the heat and work of a reversible, isothermal expansion

Answer 17

q = nRT ln (Vf/Vi)
w = -nRT ln (Vf/Vi)
q= -w

Question 18

In an expansion, Vf > Vi. The sign of q is ____ because ____

Answer 18

In an expansion, Vf > Vi. The sign of q is positive because energy flows as heat into the system to make up for energy lost as work

Question 19

The higher the temperature, ___ work is done, so ____ energy must enter as heat to make up for the energy lost.

Answer 19

↑T = ↑ +q (heat absorb) = ↑ -w (work done)

Question 20

The grand total energy of the system. Give the formula for its change

Answer 20

Internal energy (U)
ΔU = w + q

Question 21

What is the change in internal energy for a reversible, isothermal expansion of perfect gas? What does it imply?

Answer 21

ΔU = 0
since ΔU = w + q and q = -w

the internal energy of a sample of perfect gas at a given temperature is independent of the volume it occupies.

Question 22

Define state function and how internal energy is a state function

Answer 22

State function - physical property that depends on the present state of system and is independent of the path taken

Internal energy is independent of the changes in pressure and temperature (and any other variables)

Question 23

The internal energy of an isolated system is ______

Answer 23

constant

NOTE: not zero and this is the first law of thermodynamics

Question 24

Internal energy change when the volume is constant and no non-expansion work

Answer 24

ΔU = q → ΔU = qv
since w = 0

Question 25

A bomb-calorimeter is an example of ____ calorimeter. The arrangement of the vessel and the water bath ensures a/an ____ system

Answer 25

constant-volume calorimeter adiabatic system - no heat transfer

Question 26

Constant-volume heat capacity formula. Give the relationship of internal energy and temperature

Answer 26

Cv = ΔU / ΔT from C = q / ΔT and ΔU = q since constant-volume (no work) As ↑T, ↑U in a curve (the slope is the heat capacity)

Question 27

The internal energy is the total energy of a system that takes into account the populations of the _____.

Answer 27

allowed energy states At low temperatures, molecules occupy only states of low energy; as the temperature increases, they occupy more of the higher energy states.

Question 28

Define equipartition theorem

Answer 28

each degree of freedom (n) of a molecule gets an equal amount of energy — specifically, ½ kT of energy per molecule => E = n (1/2kT) for translation and rotation while E = n (kT) for vibration