Rate and extent of chemical change

Question 1

why are rates of reaction important in the chemical industry?

Answer 1

The faster you can make chemicals, the faster you make money

Question 2

What is the rate of a chemical reaction?

Answer 2

The rate of a chemical reaction is how fast the reactants are changed into products

Question 3

give an example of a slow reaction:

Answer 3

• rusting of iron
• chemical weathering

Question 4

give an example of a moderate reaction:

Answer 4

• magnesium reacting with an acid to produce a stream of bubbles

Question 5

give an example of a fast reaction:

Answer 5

• burning
• explosions

Question 6

How to find the rate of reaction?

Answer 6

by recording the amount of product formed, or the amount of reactant used up over the time period

Question 7

On a graph for rate of reaction, what does the steeper the line mean?

Answer 7

The faster the rate of reaction

Question 8

On a graph for rate of reaction, what do the quickest reactions look like?

Answer 8

The steepest line and become flat in the shortest time

Question 9

what does the rate of reaction depend on?

Answer 9

• temperature
• concentration of solution or pressure of gas
• surface area of solid
• the presence of a catalyst

Question 10

how does increasing the temperature increase the rate of reaction?

Answer 10

Increasing the pressure means the particles move faster. This means there are more frequent successful collisions so the reaction will happen quicker

Question 11

how does increasing the concentration or pressure increase the rate of reaction?

Answer 11

Increasing the concentration/pressure means there are more particles colliding in the same volume of solvent or space. This increases the amount of frequent successful collisions

Question 12

how does increasing the surface area increase the rate of reaction?

Answer 12

more surface area increases the amount of area for collisions to happen - meaning a faster rate of reaction

Question 13

How does using a catalyst increase the rate of reaction?

Answer 13

a catalyst will not be used up in the reaction, and it is reduces the activation energy needed for the reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy. This will speed up the rate of reaction.

Question 14

what are three ways to measure the rate of a reaction?

Answer 14

1) Precipitation and colour change - record how long it takes to see a visible change
2) Change in mass - record how long it takes for the mass to increase or decrease
3) The volume of gas given off - record the amount of gas given off in a time interval

Question 15

how to find mean rate of reaction on a graph?

Answer 15

divide the overall energy change (y-axis) by the total time taken (x-axis)

Question 16

how to find rate of reaction at a particular point in time on a graph?

Answer 16

Draw a straight line - tangent - to the curve and find the gradient

Question 17

How does a reversible reaction reach equilibrium?

Answer 17

1) as the reactants react, their concentrations will fall so the forward reaction slows down
2) as more products are made and their concentrations rise, the backwards reaction will speed up
3) after a while the forward and backward reaction will go at the same rate - this is at equilibrium

Question 18

what is happening at equilibrium?

Answer 18

at equilibrium, both reactions are happening but there is no overall effect (its a dynamic equilibrium) This means the concentrations of reactants and products have reached a balance and won’t change - for equilibrium to be reached, it must be a closed system

Question 19

What is a closed system?

Answer 19

None of the reactants or products can escape and nothing else can enter the reactions

Question 20

Where can the position of equilibrium be?

Answer 20

to the right - concentration of products is greater than the reactants
to the left - the concentration of reactants is greater than the products