A mixture of C2H4(g) and H2(g) is placed in a sealed container. Some finely divided nickel is added as a catalyst to the mixture. The temperature rises to 150°C and the two gases slowly react to give C2H6(g). Which row of the table correctly identifies how the pressure changes after the nickel is added?

Answer:

26) E

Since temperature is proportional to pressure, pressure will initially increase to allow both gases to react.

Now let us write out the reaction equation

C₂H₄ + H₂  ->  C₂H₆

Using the equilibrium rules, we can see that moles of products is ½ of moles of reactants. This means that as the reaction progresses, pressure will decrease.

Hence, E is the answer.