[jsmith613]

Q1) If I were to have a reaction as follows
A (g) + B(l) --> <-- 2C (g) + D (g)
Would pressure have any effect

Essentialy, what I am asking is do all reactants / products need to be gaseous for equilibrium to shift due to pressure changes

Q2)
Why is the rate of reaction unaffected by a change in PRESSURE in a heterogeneous catalysed reaction

THANKS

[scientifics]

Pressure affects equilibrium even if you don't have only gases (as long as the number of moles gas isn't equal, and the gas is reactive), however, the answer to this question lies in the fact that the reaction involves a catalyst.  What does a catalyst do (how does it take part in the reaction) and how does it affect the rate?

[jsmith613]

What does a catalyst do (how does it take part in the reaction) and how does it affect the rate?

It provides an alternate route with no effect on rate
BUT a PRESSURE CHANGE in a catalysed reaction (heterogenous) has no effect? Why?

[scientifics]

The use of a catalyst decreases the activation energy, so it increases the rate of the reaction, both forward and reverse.  The change in pressure pushes the equilibrium to the left (LeChatlier's principle - increased pressure shifts the equilibrium to the left).

[jsmith613]

yes but generally increasing pressure increases rate of reaction
why would the rate of heterogenously catalysed reaction be unaffected by a change in pressure

[DevaDevil]

yes but generally increasing pressure increases rate of reaction

only for reactions with gaseous reactants, if the catalyst phase is not gaseous, the pressure dependence will be limited