5A - The rate equation

Question 1

define Order of a reaction

Answer 1

The power to which the concentration of a reactant is raised in the rate equation

Question 2

define Overall Order of a reaction

Answer 2

The sum of the individual orders of the reactants in the rate equation, m+n

Question 3

define Rate constant, k

Answer 3

The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation

Question 4

define Half-life

Answer 4

The time taken for the concentration of a reactant to decrease by half

Question 5

define Rate-determining step

Answer 5

The slowest step in the reaction mechanism of a multi-step reaction

Question 6

Write out the formula from the rate equation

Answer 6

Rate = k [A]^m [B]^n

Question 7

Which reactants appear in the rate equation?

Answer 7

The reactants that are present in the rate-determining step

Question 8

What happens to the rate of reaction when you double the concentration of a reactant that is: a. Zero Order b. First Order c. Second Order

Answer 8

The rate will: a. Stay the same b. Double c. Quadruple

Question 9

Rearrange the rate equation to give k

Answer 9

k = rate / [A]m [B]n

Question 10

Sketch the shape of a concentration-time graph for: a. A Zero Order reaction b. A First Order reaction c. A second order reaction

Answer 10

Graphs:

Question 11

Which concentration-time graph has a a decreasing, constant, and increasing half-life?

Answer 11

decreasing: zero constant: first increasing: second

Question 12

Give the equation used to find k from the graph with the constant half-life.

Answer 12

k = ln 2 / t1/2

Question 13

How would you find k from a Zero Order concentration-time graph?

Answer 13

Calculate the gradient

Question 14

How would you find k on a Zero Order and on a First Order rateconcentration graph?

Answer 14

Zero Order = y-intercept First Order = gradient

Question 15

What graph could you draw for a Second Order reaction that would allow you to calculate k directly from the graph?

Answer 15

Plot a graph of rate – concentration squared (rate- [X]^2 ) and then calculate the gradient

Question 16

How could you propose a plausible reaction mechanism?

Answer 16

(1) Use the rate equation to find the species in the Rate Determining Step (2) Suggest a series of steps with no more than TWO colliding particles

Question 17

How does an increase in temperature affect the rate constant?

Answer 17

As the temperature increases, so does the rate constant

Question 18

Why does the rate of reaction increase as the temperature is increased?

Answer 18

The proportion of molecules with an energy greater than or equal to the activation energy (E ≥ Ea) increases and the kinetic energy of the particles increases, causing more frequent collisions.

Question 19

Write out the ln form of the Arrhenius Equation in the form y= mx+c

Answer 19

Ln k = -Ea/R x 1/T + ln A y = ln k m = -Ea/R x = 1/T c = ln A

Question 20

. Sketch the shape of a rate-concentration graph for: a. A Zero Order reaction b. A First Order reaction c. A Second Order reaction

Answer 20