Free Reaction Kinetics MCQs with Answers
23 Reaction Kinetics MCQs from Chemistry, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
23 questions · page 3 of 3
21. Amount of energy needed to weaken the existing bonds to an extent that can be broken through collision is called:
- A. Bond energy
- B. Activation energy
- C. Average energy
- D. Enthalpy
Explanation: Activation energy is the barrier reactant molecules must climb to reach the transition state, and only collisions carrying at least this much energy, with the right orientation, lead to reaction. Bond energy is the energy needed to break a particular bond completely in the gaseous state, a different quantity. A catalyst works by lowering the activation energy, not the bond energy.
Correct answer: Activation energy22. 2A + B gives 3C + D. Which of the following does not express the reaction rate?
- A. -d[B]/dt
- B. d[D]/dt
- C. -1/2 d[A]/dt
- D. -1/3 d[C]/dt
Explanation: Rate is expressed as the change in concentration divided by the coefficient, with a minus sign for reactants because they are being consumed and a plus sign for products because they are being formed. C is a product, so its term must be positive, and writing it with a minus sign makes the expression wrong. The other three all give the same positive rate.
Correct answer: -1/3 d[C]/dt23. Final equation for the representation of rate of reaction in term of concentration is called
- A. Rate law
- B. Rate constant
- C. Reaction rate
- D. Reaction order
Explanation: The rate law, or rate equation, states the rate as the rate constant multiplied by concentration terms raised to their experimentally determined powers. The rate constant is only the proportionality factor within it and the order is the exponent, so both are components of the rate law rather than the equation itself. Orders must be found by experiment, since they need not match the coefficients in the balanced equation.
Correct answer: Rate law