Question

Equal volumes of CO and O₂ are kept in a closed cylinder under certain temperature and pressure. The mixture is heated till all the CO gets converted to CO₂ . Then, the temperature of the gases is brought to the previous temperature. Will there be any change in any parameter of the gas or gases present in the cylinder? Justify your answer with appropriate reasons. If any change takes place, calculate the percentage change.?

Answer 1

$2\mathrm{CO}+{\mathrm{O}}_2\to 2{\mathrm{CO}}_2$

• According to the above equation, 2 molecules of CO combine with 1 molecule of O₂ to form 2 molecule of CO₂ .
• In general, 2n molecules of CO combine with n molecule of O₂ to form 2n molecules of CO₂.
• After the reaction, 2n molecules of CO₂ is formed and n molecules of O₂ left behind.
• When the volume is fixed and temperature brought into previous temperature, the number of molecules will be reduced.
• Hence pressure will be reduced.
• Initial pressure (P₁) depends on number of reactant molecules.
• Initially there are 4 molecules (2CO and 2O₂)
• P₁ = 4x
• Final pressure (P₂) depends on number of molecules left behind.
• There are 3 molecules left behind. (2 CO₂ molecule and one unreacted O₂ molecule.)
• P₂ = 3x
• Change in pressure = $\frac{4\mathrm{x}-3\mathrm{x}}{4\mathrm{x}}$

= $\frac{\mathrm{x}}{4\mathrm{x}}=\frac{1}{4}=0.25$

• Percentage change in pressure = $0.25\times 100$

= 25%