# Chapter 18: Rates of Reaction (18.1 - 18.5) Flashcards

1
Q

define rate of reaction

A

the change in concentration of a reactant or product in a given time

2
Q

equation for rate of reaction

A

rate = change in concerntration / change in time

3
Q

what is order

A

order shows how rate is affected by the concentration

for order n: rate ∝ [A]^n

4
Q

zero order

A

rate ∝ [A]^0
rate is not affected by the concentration
horizontal line on a rate/conc graph
downward linear on a conc/time graph

5
Q

first order

A

rate ∝ [A]^1
rate changes by the same factor as concentration
upward linear relationship with line going through origin on a rate/conc graph
downward curve asymptotic to y=0 for conc/time graph

6
Q

second order

A

rate ∝ [A]^2
rate changes by the same factor as the concentration change squared
upwards steep curved line starting at origin on a rate/conc

7
Q

find reaction rate from a conc/time graph

A

take a tangent

gradient of tangent = rate of reaction

8
Q

what is overall order

A

the sum of the individual orders of the reactants.
eg for reactants A and B with orders m and n (respectively)
overall order = m + n

9
Q

the rate equation:

ie for reaction A + B –> C with orders m (for A) and n (for B) what is the rate given by

A

rate = K X [A]^m X [B]^n

k = rate constant

10
Q

units for rate

A

moldm^-3s^-1

11
Q

to work out units of K

A
• rearrange the rate equation to make K the subject
• substitute units into the rearranged rate equation
• cancel common units and write the final units on a single line
12
Q

define half-life

A

the half-life of a reactant is the time for its concentration to decrease by half

13
Q

whats special about first order reactions

A

first order reactions have a constant half-life

K = ln2 / halflife (s)

14
Q

what is a colorimeter and what is it used for

A
```A colorimeter measures the intensity of light passing through a sample.
Absorbance reading is directly linked to the concentration of the solution (when either the reactant or product is coloured and the other is colourless)
eg Br2 (coloured) --> 2Br- (colourless)```
15
Q

what is the rate-determining step

A

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

16
Q

Why is it unlikely that the reaction would take place in one step?

A

1) Usually only two molecules would collide at once

2) The stoichiometry of the equation would not balance

17
Q

How do you predict the reaction mechanism of an equation?

A

1) The rate equation only includes reacting species

2) The orders in the rate equation match the number of species involved in the rate determining step

18
Q

What is the Arrhenius equation?

A

K = Ae^-Ea/RT

19
Q

What do the symbols in the Arrhenius equation stand for?

A

A - pre exponential factor
Ea - activation energy
R - gas constant
T - temperature in kelvin

20
Q

Logarithmic form of Arrhenius equation

A

Lnk = (-Ea/R)(1/T) + lnA

• intercept of c = lnA
21
Q

What effects the rate constant?

A
• Increasing temperature, increases rate constant and decreasing activation energy, increases rate constant due
• Boltzmann distribution shifting to the right when temperature increases and both cause an increase in the number of particles with energy above activation energy.
22
Q

What is the rate constant?

A

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

23
Q

How can you work out rate constant from first order rate-conc graph?

A