Thermal Processes in Gases: Lab Work

Laboratory Work: Study of Thermal Processes in Gases

• Objective: Study thermal processes in gases using a PhET simulation. Measure and compare heat capacities at constant volume (Cv) and constant pressure (Cp). Verify the relationship Cp-Cv = R experimentally.

Equipment

• Computer with internet access.
• PhET Interactive Simulation: Gas Properties.

Theory

• Heat Capacity (Cv): Amount of heat required to raise the temperature of a gas while keeping the volume constant.
• Heat Capacity (Cp): Amount of heat required to raise the temperature of a gas while keeping the pressure constant.
• Relationship Between Cp and Cv: Cp - Cv = R, where R is the universal gas constant (8.314 J/mol·K).
• Adiabatic Index (γ): γ = Cp/Cv, describing the relationship between heat capacities .
• First Law of Thermodynamics: ∆U = Q - W. For constant volume, W = 0, so ∆U = Q. For constant pressure, Q = ∆U + W.

Procedure:

• Step 1: Accessing the Simulation: Open the PhET Gas Properties simulation and set it to the Ideal Gas Behavior mode.
• Step 2: Experiment for Constant Volume: Select a gas (e.g., Neon). Set a fixed volume. Set a low heater power. Record initial and final temperatures (T1 and T2). Calculate the heat added (Q).
• Step 3: Experiment for Constant Pressure: Allow the gas to expand while keeping the pressure constant. Repeat the heating process as in Step 2, recording T1 and T2. Calculate Cp.
• Step 4: Verification: Verify the relationship Cp - Cv = R and calculate the adiabatic index (y).

Observations

• Record data including initial temperature, final temperature, heat added, and whether the experiment was at constant volume or pressure.

Theoretical Questions

• Define heat capacity, specific heat capacity, and molar heat capacity. Explain the difference between Cv and Cp and why Cp > Cv.
• State the first law of thermodynamics and how it applies to isochoric (constant volume) and isobaric (constant pressure) processes.
• Derive the relationship Cp - Cv = R for an ideal gas.
• What is an adiabatic process and how does it differ from isochoric process?
• What assumptions are made in the ideal gas law and how do these affect the accuracy of heat capacity measurements?
• Define the adiabatic index (γ) and why it is important.
• How do degrees of freedom affect heat capacities?
• How is heat capacity related to the internal energy of an ideal gas?

Problems

(These are specific calculation problems based on the given data, so there is no direct answer possible without that data.)