(455) HL Thermodynamic processes [IB Physics HL]
Thermodynamic Processes Overview
Focus on work and energy relations.
Reference: "When you really want to play hard without working hard" (The Office).
Key Concepts
First Law of Thermodynamics
Energy transfer relates to change in internal energy (ΔU) and work done.
Work done (W) = P ΔV (area under PV diagram).
Rightward movement = Positive work.
Leftward movement = Negative work.
Ideal Gas Equation
P = nRT
As temperature increases, internal energy (ΔU) increases.
Types of Thermodynamic Processes
1. Isovolumetric Process (Constant Volume)
PV = nRT; volume is constant.
Pressure (P) is proportional to temperature (T).
Graph: P vs. T is a straight line.
Increasing T leads to increasing P and vice versa.
Change in Internal Energy (ΔU): If P decreases, T decreases → ΔU is negative.
Work done (W): Area under curve is zero → W = 0.
Heat transfer (Q): Q = ΔU + W → Q is negative.
2. Isobaric Process (Constant Pressure)
Ignore pressure in PV = nRT; focus on volume.
Volume is proportional to temperature.
As temperature increases, volume increases.
ΔU: If volume increases, T increases → ΔU is positive.
Work done (W): Positive area under the graph → W is positive.
Heat transfer (Q): Q = ΔU + W → Q is positive.
3. Isothermal Process (Constant Temperature)
Ignore temperature in PV = nRT; focus on pressure and volume.
Pressure is proportional to 1/volume.
As pressure decreases, volume increases.
ΔU: If T is constant, ΔU = 0.
Work done (W): Area under the curve → W is negative.
Heat transfer (Q): Q = ΔU + W → Q is negative.
4. Adiabatic Process
Q = 0 (no heat transfer).
Looks similar to isothermal but steeper.
Work done (W): Area is positive, moving to the right.
ΔU: Based on the relation Q = ΔU + W, if Q is zero, ΔU must be negative, because it compensates for the positive work done.
Adiabatic pressure relation: PV^(5/3) = constant for ideal monatomic gas.
Link between states: P_A * V_A^(5/3) = P_B * V_B^(5/3).
Useful for solving thermodynamic problems efficiently.