In the combined gas law, which variable is assumed to remain constant?

• A. The temperature (T)
• B. The pressure (P)
• C. The amount of gas (n)
• D. The volume (V)

Answer: (C)

Verified step by step guidance

1. Recall that the combined gas law relates pressure (P), volume (V), and temperature (T) of a gas sample, and is expressed as \(\frac{P_1 V_1}{T_1} = \frac{P_2 V_2}{T_2}\).
2. Notice that the combined gas law does not include the amount of gas (n) explicitly, which means it assumes the amount of gas remains constant during the process.
3. Understand that the combined gas law is derived from combining Boyle's law, Charles's law, and Gay-Lussac's law, all of which consider a fixed amount of gas.
4. Therefore, when using the combined gas law, the variable that is held constant is the amount of gas (n), while pressure, volume, and temperature can change.
5. Summarize that the combined gas law is useful for problems where the quantity of gas does not change, but pressure, volume, and temperature vary.