Question

1. a gas undergoes a process where pv = constant. what type of process is this and what happens to temperature? mark only one oval. adiabatic process; temperature decreases isochoric process; temperature varies isothermal process; temperature remains constant isobaric process; temperature increases 20. when a bicycle pump gets hot during use, which energy transformation is primarily occurring? mark only one oval. chemical energy to thermal energy potential energy to kinetic energy kinetic energy of motion to thermal energy through compression electrical energy to mechanical energy 21. in a pressure cooker, food cooks faster because: * mark only one oval. adiabatic conditions prevent heat loss constant volume increases temperature lower pressure decreases cooking time higher pressure increases the boiling point of water

Explanation:

19.

• For an ideal gas, the ideal gas law is \(PV = nRT\). If \(PV=\text{constant}\), then \(nRT=\text{constant}\). Assuming the amount of gas \(n\) is constant (no gas added or removed), \(T\) (temperature) remains constant.
• An isothermal process is defined as a process where the temperature of the system remains constant.
• Adiabatic process: \(Q = 0\) (no heat transfer), not related to \(PV=\text{constant}\) for temperature constancy.
• Isochoric process: \(V=\text{constant}\), not \(PV=\text{constant}\).
• Isobaric process: \(P=\text{constant}\), not \(PV=\text{constant}\).

• When using a bicycle pump, a person does work (kinetic energy of motion) on the gas inside the pump.
• By the first law of thermodynamics \(\Delta U=Q + W\) (where \(W\) is work done on the system). Here, \(Q\approx0\) (quick process, little heat transfer), and \(W> 0\) (work done on the gas).
• The work done on the gas (compression) increases the internal energy of the gas (and the pump, as it is in contact with the gas), which is manifested as an increase in thermal energy (temperature rise).
• Chemical energy to thermal energy: No chemical reaction occurring in the pump operation.
• Potential energy to kinetic energy: Not the primary energy transformation (no significant change in height, so potential energy change is negligible).
• Electrical energy to mechanical energy: No electrical input in a basic bicycle - pump operation.

• The boiling point of a liquid is the temperature at which the vapor pressure of the liquid equals the external pressure.
• In a pressure cooker, the pressure inside is higher than atmospheric pressure.
• Using the Clausius - Clapeyron relation, as pressure \(P\) increases, the boiling point \(T_b\) of water increases.
• Higher boiling point means water can reach a higher temperature before vaporizing. Since the rate of a cooking (chemical) reaction generally increases with temperature, food cooks faster.
• Adiabatic conditions: A pressure cooker is not an adiabatic system (heat is added to cook the food).
• Constant volume: While the volume of the pressure cooker is approximately constant, it is the increase in pressure (and thus boiling point) that causes faster cooking, not just constant volume.
• Lower pressure: Lower pressure would decrease the boiling point (e.g., at high altitudes water boils at a lower temperature), which would increase cooking time.

Answer:

Isothermal process; temperature remains constant

20.