We are asked to **calculate what will be its partial ****pressure after 2.5 hours** given **the rate constant for this reaction is 2.1 × 10 ^{−4} **

We’re given the following first-order reaction:

C_{2}H_{5}NO_{2}_{(g)} → C_{2}H_{4}_{(g)} + HNO_{2}_{(g)}

The integrated rate law for a first-order reaction is as follows:

$\overline{){\mathbf{ln}}{\mathbf{\left[}\mathbf{A}\mathbf{\right]}}_{{\mathbf{t}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{\mathbf{-}}{\mathbf{kt}}{\mathbf{}}{\mathbf{+}}{\mathbf{}}{\mathbf{ln}}{\mathbf{\left[}\mathbf{A}\mathbf{\right]}}_{{\mathbf{0}}}}$

where:

**[A] _{t}** = concentration at time t

**k** = rate constant

**t** = time, **[A] _{0}** = initial concentration.

Recall that the moles of gases are proportional to the partial pressure. This means we can use the same equation and use pressure instead of concentration.

Consider the gas-phase reaction (constant volume) of the decomposition of nitroethane:

C_{2}H_{5}NO_{2}_{(g)} → C_{2}H_{4}_{(g)} + HNO_{2}_{(g)}

At 610 K, the rate constant for this reaction is 2.1 × 10^{−4 }s^{-1} initial partial pressure of C_{2}H_{5}NO_{2} is 80 torr, what will be its partial pressure after 2.5 hours?

A. 12 torr

B. 77 torr

C. 31 torr

D. 9 torr

E. 18 torr

F. 26 torr

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Integrated Rate Law concept. You can view video lessons to learn Integrated Rate Law. Or if you need more Integrated Rate Law practice, you can also practice Integrated Rate Law practice problems.