Question

Calculate the half-life of the first-order reaction
$C_{2}H_{4}O\left(g\right) \rightarrow \left(CH\right)_{4}\left(g\right)+CO\left(g\right)$
if the initial pressure of $C_{2}H_{4}O\left(g\right)$ is $80mm$ and the total pressure at the end of $20$ minutes is $120mm$

• A. $40min$
• B. $120min$
• C. $20min$
• D. $80min$

Answer 1

Answer: (C)

$C_{2}H_{4}O\left(g\right) \rightarrow \left(CH\right)_{4}\left(g\right)+CO\left(g\right)$
Initially 80 mm 0 0
After 20 minutes 80-y y y
Total pressure = 80-y +y+y = 80 + y = 120
y = 40
50% of reactant decomposed within 20 minutes, so half life will be 20 minutes.