How does pressure affect the rate of a gaseous reaction?

In summary, the rate equation for a gaseous reaction A2 + B2 -> 2C is rate = k[A2]2[B2]. If the reaction mixture is compressed to half its original volume, the reaction rate will increase by a factor of 8, but the rate equation remains the same. This is because the concentration of the reactants, represented by [A2] and [B2], is still the same, only the pressure has changed.
  • #1
absolutezer0es
14
0
The question is:

The rate equation for the reaction A2 + B2 -> 2C (all gases) is rate = k[A2]2[B2]. If the gaseous reaction misture is compressed to half its original volume, by what factor will the reaction rate change. Assume temperature is constant.

My thoughts are that the reaction rate wouldn't change. I know the rate changes if the concentrations of any of the reactants do, which is quite simple to calculate, but I'm not totally sure on pressure's effect on reaction rate. Any pushes in the right direction would be great.
 
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  • #2
Imagine having 1 mole of an ideal gas squeezed into 1 L volume. What is its concentration?

Apply twice the pressure. What is the volume now? What is the concentration now?
 
  • #3
Ah, I see. The concentration of both would be 2M, so substituting would give me:

rate = 8k[A2]2][B2]

Thanks for the help!
 
  • #4
absolutezer0es said:
Ah, I see. The concentration of both would be 2M, so substituting would give me:

rate = 8k[A2]2][B2]

Thanks for the help!

No! The rate has increased by a factor of 8 but it's still k[A2]2][B2] , just each of the things inside the brackets has doubled.
 
  • #5
What do you mean by "it's"? The reaction rate doesn't increase by a factor of 8?
 
  • #6
absolutezer0es said:
What do you mean by "it's"? The reaction rate doesn't increase by a factor of 8?

Yes I said the reaction rate increases 8X. "It's" means "it is". :oldsmile:

Consider [A2], [B2] to represent variables, k a constant.
 
Last edited:
  • #7
In other words, rate is in both cases k[A2]2[B2], but rate'=8*rate.
 

1. What is the relationship between reaction rate and pressure?

As pressure increases, the reaction rate also increases. This is because an increase in pressure leads to a higher concentration of reactant particles, which results in more frequent and energetic collisions, increasing the likelihood of successful collisions and a faster reaction rate.

2. How does pressure affect the rate of a chemical reaction?

Higher pressure leads to a higher rate of reaction, while lower pressure leads to a lower rate of reaction. This is due to the fact that pressure affects the concentration of reactant particles, which in turn affects the frequency and energy of collisions between particles.

3. Does pressure have a greater effect on reaction rate than temperature?

In most cases, temperature has a greater effect on reaction rate than pressure. This is because temperature directly affects the kinetic energy of particles, increasing their speed and therefore the frequency of collisions. However, pressure can still have a significant impact on reaction rate, especially in cases where the reaction is highly dependent on the concentration of reactant particles.

4. Can pressure be used to control the rate of a reaction?

Yes, pressure can be used to control the rate of a reaction. By adjusting the pressure, the concentration of reactant particles can be altered, which in turn affects the rate of reaction. This can be useful in industrial processes where precise control of reaction rate is necessary.

5. How does pressure affect the equilibrium of a chemical reaction?

Pressure does not affect the equilibrium constant of a chemical reaction, but it can affect the position of equilibrium. An increase in pressure will shift the equilibrium towards the side with fewer gas molecules, while a decrease in pressure will shift it towards the side with more gas molecules. This is due to Le Chatelier's principle, which states that a system will shift in a direction that reduces the stress placed upon it.

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