7 First Law Of Thermodynamics

Question 1

Heat capacity, C

Answer 1

Amount of thermal energy required to raise its temperature by one degree
C = Q/(θf-θi)

Question 2

Specific heat capacity, c

Answer 2

Amount of thermal energy required to raise the temperature of a unit mass of the substance by one degree
c = Q/m(θf-θi)

Question 3

Specific latent heat, L

Answer 3

Thermal energy to change phase of a unit mass of a substance, without a change in temperature
Q = mL

Question 4

Internal energy, U

Answer 4

Sum of a random distribution of kinetic and potential energies associated with the molecules of a system

Question 5

First Law of Thermodynamics

Answer 5

The increase in the internal energy of a closed system is the sum of the heat supplied to the system and the work done on the system
ΔU = Q + W

Question 6

Work done on gas

Answer 6

ΔW = pΔV
Compression: work done on gas
Expansion: work done by gas

Question 7

Isothermal process

Answer 7

ΔT=0, hence ΔU=0
Hence Q=-W OR -Q=W

Question 8

Iso-volumetric process

Answer 8

ΔV=0, hence W=0
Hence ΔU=Q

Question 9

Isobaric process

Answer 9

Δp=0, W=area under pV graph

Question 10

Adiabatic process

Answer 10

Q=0, hence ΔU=W