When gases are heated from 20 to 40ºC at constant pressure, their volumes — States of Matter and Gaseous State Chemistry Question

💡 Solution & Explanation

# Solution: Volume Change of Gases with Temperature at Constant Pressure **Given Information:** - Initial temperature: $T_1 = 20°C = 293 \text{ K}$ - Final temperature: $T_2 = 40°C = 313 \text{ K}$ - Pressure is constant **Apply Charles's Law:** At constant pressure, volume is directly proportional to absolute temperature: $$\frac{V_1}{T_1} = \frac{V_2}{T_2}$$ **Calculate the volume ratio:** $$\frac{V_2}{V_1} = \frac{T_2}{T_1} = \frac{313}{293} = 1.068$$ This means $V_2 = 1.068 \times V_1$ **Percentage increase in volume:** $$\text{% increase} = \left(\frac{V_2 - V_1}{V_1}\right) \times 100 = (1.068 - 1) \times 100 = 6.8\%$$ **Conclusion:** When gases are heated from 20°C to 40°C at constant pressure, their volumes **increase by approximately 6.8%** (or ~7%). This follows Charles's Law, which states that gas volume increases proportionally with absolute temperature when pressure remains constant. *Option D likely states "increase" or gives the ~7% increase value.*