As the temperature increases, the density of a gas does what?

As the temperature increases, the density of a gas does what?

• A. Increases
• B. Stays the same
• C. Decreases
• D. Increases then decreases

Answer: (C)

When a gas is heated at constant pressure, it expands. According to PV = nRT, for fixed pressure and a fixed amount of gas, increasing temperature requires a larger volume. Density is mass per volume, so with the same amount of gas and a bigger volume, density decreases. That’s why the correct statement is that density decreases as temperature rises. The idea that density would increase would imply the gas becomes more concentrated, which doesn’t happen when it expands at the same pressure. Keeping density the same would require no change in volume or a change in pressure that exactly offsets the temperature change, which isn’t part of the standard scenario. The “increases then decreases” option isn’t supported by a simple temperature rise without another changing factor.

When a gas is heated at constant pressure, it expands. According to PV = nRT, for fixed pressure and a fixed amount of gas, increasing temperature requires a larger volume. Density is mass per volume, so with the same amount of gas and a bigger volume, density decreases. That’s why the correct statement is that density decreases as temperature rises.

The idea that density would increase would imply the gas becomes more concentrated, which doesn’t happen when it expands at the same pressure. Keeping density the same would require no change in volume or a change in pressure that exactly offsets the temperature change, which isn’t part of the standard scenario. The “increases then decreases” option isn’t supported by a simple temperature rise without another changing factor.