Reaction rates and enthalpy

Written by Dr. Ayesha Nadeem (Chemistry)

ECAT · Chemistry · 5 questions

Name: ____________________ Date: ____________

What are the units of the rate constant of a first order reaction?
- A mol s
- B dm^3 mol^-1 s^-1
- C s^-1
- D mol dm^-3 s^-1
According to the Arrhenius equation, raising the temperature:
- A Decreases the rate constant
- B Increases the rate constant
- C Makes the activation energy negative
- D Has no effect on the rate constant
The enthalpy of neutralisation of a strong acid with a strong base is about:
- A -570 kJ/mol
- B +57 kJ/mol
- C 0 kJ/mol
- D -57 kJ/mol
The order of a reaction can be determined:
- A From the molar mass
- B From the colour of the products
- C From the balanced equation alone
- D Only by experiment
For a reaction with rate = k[A]^2, doubling [A] makes the rate:
- A Double
- B Eight times as large
- C Unchanged
- D Four times as large

Answer key

1. C, 2. B, 3. D, 4. D, 5. D

Rate = k[A] gives k = rate / concentration, whose units are s^-1.
A higher temperature puts more molecules above the activation energy, so k increases.
The reaction is H+ + OH- giving water, and it releases about 57 kJ per mole of water formed.
The order depends on how the rate changes with concentration, which has to be measured.
The rate is proportional to [A] squared, so doubling [A] multiplies the rate by 4.