Ammonia is used to make fertilizer. The Haber process produces ammonia, NH3, fro

Question

Ammonia is used to make fertilizer. The Haber process produces ammonia, NH3, from N2 and H2. This reaction has an equilibrium constant of 4.31*10^-4 at 375 degrees C. This reaction is exothermic.

A. N2 and H2 are placed in a container and heated to 375 degrees C. Will a reaction occur? if so, do you the the % yeild will be high or low? give reasons.

B. Would you expect delta G for this reaction to be greater than 0 or less than 0? Give reasons.

C. Does K eq increase, decrease, or stay the same Temperature?

D. The Haber process uses a catalyst and product is removed during the reaction. Why is a catalyst used rather than raising the reaction temperature?

Explanation / Answer

for the reaction N2+3H2 <----->2NH3, K = [NH3]2/ [N2][H2]3 =4.31*10-4 at 375 deg.c

since equilibrium constant is very less, either concentration of products is less at equilibrium and concentration of reactants is high. This suggests the % yields is less.

delltaG= -RT lnK= -8.314*(375+273)*ln(4.31*10-4)=18132 Joules= 18.132 KJ>0. The reaction is not spontaneous.

Equilibrium constant is a function of temperature only.

the reaction is exothermic N2+3H2 -->2NH3, deltaH=-ve. So as temperature is increased, the reaction rate increases. However, the reaction proceeds in endothermic direction so so formed ammonia starts decomposing to N2 and H2. So this will reduce the conversion. So instead of increasing the temperature, catalyst is used.

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