First Law of Thermodynamics Flashcards
What is heat capacity
Heat capacity of a body is defined as the quantity of heat absorbed or liberated by the body per unit temperature change
C=Q/Δθ
What is specific heat capacity
Specific heat capacity of a material is defined as the quantity of heat absorbed or liberated per unit mass of the material per unit temperature change
c = Q/mΔθ
What is latent heat
Latent heat is defined as the quantity of heat absorbed or liberated by a substance in order to change the substance from one phase to another phase without a temperature change
What is specific latent heat of fusion
Specific latent heat of fusion of a substance is defined as the quantity of heat energy required to convert unit mass of solid to liquid without a change in temperature
L = Q/m
What is the specific latent heat of vaporisation
Specific latent heat of vaporisation of a substance is defined as the quantity of heat energy required to convert unit mass of liquid to vapour without a change in temperatue
L = Q/m
What is internal energy
The internal energy U, of a system, is the sum of random distribution of kinetic and potential energies associated with the molecules of a system
U = ΣK.E + ΣP.E.
What is the internal energy of an ideal gas
For an ideal gas, there are no intermolecular forces. Therefore, the potential energy of the molecules is zero. Internal energy = total KE
U = 3/2 NkT = 3/2 nRT = 3/2 pV
What is the first law of thermodynamics?
The first law of thermodynamics states that the increase in internal energy of a system is equal to the sum of heat supplied to the system and the work done on the system
ΔU = Q + W
- Can replace W with W(on) to remind that term in the equation is the work done on the system
What does the area under the p-V graph represent?
Work done by the gas
When a gas is brought round a complete cycle, there is ________
no net change in internal energy.
ΔU = 0
The net work done W = area enclosed by the cycle ABCA
What is isochoric process (straight vertical line in p-v graph)
- Volume is kept constant
- W = 0
- ΔU = Q
- Any heat, Q, added or extracted results in ΔU.
- Since U changes, T also changes
What is isobaric process (straight horizontal line in P-V graph)
- Pressure is kept constant
- Work done = PΔV = P(Vf - Vi)
- W is -ve during expansion, +ve during compression
- All terms of ΔU = Q + W are non-zero
What is isothermal process
- temperature is kept constant
- ΔU=0
- Q = Won = Wby
- Isothermal expansion —> Q is converted to work done by has
- Isothermal compression —> Q extracted from system = work done on gas
What is adiabatic process
- System is well-insulated or lagged so no heat can enter or escape
- Q = 0
- ΔU = W
- In adiabatic expansion, W is -ve so ΔU is -ve —> temperature decreases, gas cools
- In adiabatic compression, W is +vs so ΔU is +vs —> temperature increases, gas is hotter
