Questions 37 and 38 refer to the following information.The kinetics of a chemical reaction can be described by the equations above,
where e is a constant approximately equal to 2.718, k is the rate constant in
L/mol-s, Ea is the activation energy in J/mol-K, T is temperature in Kelvin, r is
the reaction rate in mol/s, and [A] is the concentration of a species in mols/L,
either initially as [A] 0 , or at a given time of t as [A]t. C is a constant equal to 4,
and R is a constant of 8.314 J/mol.37.If the reaction initially starts with 2 mol/L of species A, and the activation energy of the
reaction is 10,082 J/mol, at 310 Kelvin, how many seconds will it take for the
concentration of A to reach 0.4 mol/L?38.If rate constant k triples for the reaction described in question 37, what is the
concentration of species A after 50 seconds, in mol/L?Here’s How to Crack It
As you can see, in order to have a chance at solving question 38, you first must solve question 37. In most
cases, the two Extended Thinking questions will be more independent of each other. In that case, if one is
easier than the other, maybe try that one and skip the other one. Only students aiming for a top score
should attempt both Extended Thinking questions.
Tackling Extended Thinking Questions
Most Extended Thinking
questions can be solved
independent of one
another, and one is often
easier than the other.
Consider doing the more
straightforward one and
skipping the more difficult
or time-consuming one.Let’s start with question 37. There are three equations, so it is hard to know where to begin. Start by
writing down the values for the variables you know. The question tells us that [A] 0 = 2 and [A]t = 0.4. You