In a closed system, which factors affect pressure?

In a closed system, which factors affect pressure?

• A. Mass Changes and Heat Transfers
• B. Volume Changes Only
• C. External Pressure Changes Only
• D. Kinetic Energy Changes Only

Answer: (A)

Pressure inside a closed system is set by how much material is present in the gas phase and how energetic that material is. If the amount of gas changes due to internal processes (for example, a reaction that produces gas or consumes gas, or a phase change that shifts material into or out of the vapor phase), the number of gas molecules changes, which directly changes pressure at a given volume. Heat transfer changes the system’s temperature, and since temperature is a measure of the average molecular kinetic energy, adding or removing heat alters pressure as well (for a fixed volume, higher temperature raises pressure; with a variable volume, pressure adjusts according to how temperature, amount of gas, and volume interact). Volume changes or external boundary pressures are boundary conditions rather than intrinsic internal factors, so the internal factors most directly altering pressure in a closed system are changes in the amount of gas (mass changes within the system) and changes in temperature due to heat transfer.

Pressure inside a closed system is set by how much material is present in the gas phase and how energetic that material is. If the amount of gas changes due to internal processes (for example, a reaction that produces gas or consumes gas, or a phase change that shifts material into or out of the vapor phase), the number of gas molecules changes, which directly changes pressure at a given volume. Heat transfer changes the system’s temperature, and since temperature is a measure of the average molecular kinetic energy, adding or removing heat alters pressure as well (for a fixed volume, higher temperature raises pressure; with a variable volume, pressure adjusts according to how temperature, amount of gas, and volume interact). Volume changes or external boundary pressures are boundary conditions rather than intrinsic internal factors, so the internal factors most directly altering pressure in a closed system are changes in the amount of gas (mass changes within the system) and changes in temperature due to heat transfer.