# HELP, Reaction Rate?

## Write a balanced equation for the combustion of heptane at 25 o C (not in a closed system). State how the reaction rate will be affected and give a reason for each prediction if a) oxygen is added at constant volume b) catalyst is added c) the reaction mixture is expanded d) carbon dioxide is added at constant volume e) the temperature is lowered

May 24, 2018

This question requires a fairly good understanding of kinetics and equilibrium.

Consider,

${C}_{7} {H}_{16} + 11 {O}_{2} r i g h t \le f t h a r p \infty n s 7 C {O}_{2} + 8 {H}_{2} O$

If oxygen is added at constant volume, $p {O}_{2}$ increases, the rate will generally increase.

If a catalyst is added, it will lower the activation energy by providing an alternative pathway, and increase the rate.

If the reaction mixture is expanded, the reactants' density in space will decrease, less collisions will occur, and the rate will decrease.

If carbon dioxide is added at constant volume the equilibrium will shift left (Le Chatlier's principle) and the rate would probably decrease by some factor.

If the temperature is lowered, a smaller distribution of the population of reactant molecules will have the requisite kinetic energy to collide at the right speed to react. Hence, the rate will decrease.