Order of Reaction - Rates of Reaction (1.3)

Question 1

Increasing the concentration of a reagent always increases the rate of the reaction. True or false?

Answer 1

False. This does not always increase the rate of the reaction.

Question 2

In a multi-step reaction, what determines the overall rate of the reaction?

Answer 2

The rate determining step (RDS)

Question 3

What is the rate determining step also known as?

Answer 3

Slow step

Question 4

In an SN1 reaction, how does increasing the concentration of the Nu (nucleophile) affect the rate of reaction?

Answer 4

It does not have an effect on the rate of reaction

Question 5

What does the rate equation tell you?

Answer 5

• How the rate changes when you vary the concentration of each reactant
• The most efficient method of increasing the rate of reaction

Question 6

How can you determine the rate equation?

Answer 6

You need to carry out experiments to see how rate changes with concentration

Question 7

What does the order of reaction with respect to a reagent tell you?

Answer 7

The number particles of the reagent involved in the RDS

e.g if 1st order there is 1 molecule in the RDS (& 0 order means there are no molecules in the RDS)

Question 8

How do you work out the overall order of the reaction?

Answer 8

By adding up the individual orders w/ respect to all reactants

Question 9

If it is 1st order w/ respect to a reagent, what does this tell you about the effect of concentration (of this reagent) on rate?

Answer 9

As the concentration of the reagent doubles, the rate also doubles

Question 10

If it is 2nd order w/ respect to a reagent, what does this tell you about the effect of concentration (of this reagent) on rate?

Answer 10

As the concentration of this reagent doubles, the rate quadruples

Question 11

If it is 0 order w/ respect to a reagent, what does this tell you about the effect of concentration (of this reagent) on rate?

Answer 11

Changing the concentration of the reagent has no effect on the rate

Question 12

How do you determine the order of a reaction? (in an experiment)

Answer 12

You need to measure the rate of reaction & see how it changes as you alter the concentration of each reagent

Question 13

Suggest one reason why working out the rate equation of a reaction can be useful

Answer 13

• Working out how a reaction takes place (e.g in the body)
• Find the best way to optimise a reaction (e.g industrially)
• Determining how much time has passed since a reaction started (e.g forensics, radioactive decay etc.)

Question 14

What is the rate of a reaction & what are its units?

Answer 14

The change in concentration of reactants or products as a function of time

Units: mol dm-3 s-1

Question 15

How do you calculate the rate of a reaction?

Answer 15

Change in concentration of reactants or products/time taken for reaction

Question 16

Give 3 ways in which you can measure rate

Answer 16

• Titration (to find the concentration of the reactant at diff. times)
• Colorimetry (to find the conc. of a coloured species)
• pH measurements (where the pH changes w/ time)
• Pressure or volume (where a gas is made during the reaction)

Question 17

How do you find the initial rate of the reaction?

Answer 17

• Draw a concentration vs. time graph

- The initial rate is the gradient of a tangent to the curve at the start of the reaction