1. Do we include a catalyst when writing donw the rate equation?
2.Explain the following observations as fully as you can.
When ammonia is passed over a platinum gause, the rate of decompisition into nitrogen and hydrogen is independent of the partial pressure of ammonia. However, at very low pressure, the rate is directly proportional to the partial pressure of ammonia.
Just these 2 questions, thanks.
Q2 is slightly easier to answer
platinum is a catalyst. it has "spaces" /active sites for the reactants to bind, in this case ammonia. When there is a lot of ammonia, all the sites are occupied by ammonia, the rate depends on how fast Pt can catalyse the reaction
When there is little NH3, rate depends on how fast NH3 can occupy the active site..
Originally posted by Audi:1. Do we include a catalyst when writing donw the rate equation?
2.Explain the following observations as fully as you can.
When ammonia is passed over a platinum gause, the rate of decompisition into nitrogen and hydrogen is independent of the partial pressure of ammonia. However, at very low pressure, the rate is directly proportional to the partial pressure of ammonia.
Just these 2 questions, thanks.
1. Yes. Since the rate of reaction is affected by the presence and molarity of a catalyst. For any given reaction, the rate constant k is said to be affected only by temperature. This is true. But when a catalyst is employed, the reaction pathway involves an alternate mechanism with a lower activation energy (at the rate determining elementary step), which means to say that this may be considered a different reaction altogether, and hence has a different (a much larger) rate constant k value.
2. At sufficiently high pressure, the catalyst (ie. platinum) is saturated with its substrate (ie. ammonia, the excess reactant), and hence altering (eg. further increasing) the partial pressure (or molarity) of ammonia (ie. the excess reactant) does not alter the rate of reaction, ie. the reaction is zero order with respect to ammonia. At lower partial pressures (or molarities) of ammonia, the limiting reactant is the ammonia itself, and increasing partial pressure (or molarity) of ammonia (ie. the limiting reactant) will result in an increase in rate of reaction, ie. the reaction is first order with respect to ammonia.
Originally posted by quailmaster:Q2 is slightly easier to answer
platinum is a catalyst. it has "spaces" /active sites for the reactants to bind, in this case ammonia. When there is a lot of ammonia, all the sites are occupied by ammonia, the rate depends on how fast Pt can catalyse the reaction
When there is little NH3, rate depends on how fast NH3 can occupy the active site..
Yes, that's correct. (quailmaster posted whilst I was still typing my post)