Topic C6- The Rate Of Chemical Changes

Question 1

What is the rate of chemical reaction

Answer 1

This is how fast the reactants are changed into products

Question 2

What is an example of the slowest reaction

Answer 2

The rusting of iron

Or chemical weathering

Question 3

What do you need to understand on a graph to work out the rate of a reaction

Answer 3

You can find the speed of a reaction by recording the amount of product formed or the amount of reactant used up over time

The steeper the line on the graph the faster the rate of reaction over time the line becomes less steep as the reactants are used up

The quickest reaction has the steepest line and becomes flat in the least time

Question 4

What does the rate of a chemical reaction depend on

Answer 4

The collision frequency of reacting particles. The more collisions there are the faster the reaction is

The energy transferred during exclusion. Particles have to collide with enough energy for the collision to be successful

Question 5

What is the meaning of activation energy

Answer 5

The minimum amount of energy particles need to react

Question 6

What 4 things affect the rate of reactions

Answer 6

The temperature

The concentration of the solution or the pressure of gas

The surface area

The presence of a catalyst

Question 7

How does increasing the temperature increases the rate of reaction

Answer 7

When the temperature is increased the particles all move faster

If they’re moving faster they’re going to collide more frequently

Also the faster they move the more energy they have so more of the collisions will have enough energy to make the reaction happen

Question 8

How does the concentration or pressure increases the rate of reaction

Answer 8

If a solution is made more concentrated it means there are more particles knocking about in the same volume of water or another solution

Similarly when the pressure of a gas is increased it means that the same number of particles occupies a small space

This makes a collision between the reactant particles more frequent

Question 9

How does increasing the surface area increase the rate of reaction

Answer 9

One of the reactants is a solid 10 breaking it up into smaller pieces with its surface area to volume ratio

This means that for the same volume of the solid the particles around it will have more area to work on so there will be collisions more frequently

Question 10

How does using a catalyst increases the rate of reaction

Answer 10

A catalyst is a substance that speed up a reaction without being used up in the reaction itself. This means it’s not part of the overall reaction equation

Different catalysts are used for different reactions but they all work by decreasing the activation energy needed for the reaction to occur. They do this by providing an alternative reaction pathway with a lower activation energy

Question 11

How do you calculate the mean of reaction rate from a graph with two points

Answer 11

By finding the gradient of the two points

Question 12

How do you calculate the mean reaction rate from a graph with one point

Answer 12

Draw a tangent to the point in the question

Next to work out the gradient of that line

Question 13

How would reversible reactions reach equilibrium

Answer 13

As the reactants react the concentration full-so the forward reaction will slow down but as more and more products are made and their concentration rises the backward reaction will speed up

After a while the forward reaction Will be going at exactly the same rate as the backward one-the system is at equilibrium

At equilibrium both reactions are still happening but there is no overall affect. This means the concentration of reactants and products have reached a balance and won’t change

Equilibrium is only reached if the reversible reaction takes place in a closed system. A closed system just means that none of the reactants or products can escape and nothing else can get in

Question 14

What does the position of equilibrium (Amount of reactants and products) depend on

Answer 14

Temperature

The pressure (This only affects equilibriums involving gases)

The concentration of the reactants and products

Question 15

What are reversible reactions like in terms of endothermic and exothermic reaction

Answer 15

In reversible reaction if the reaction is endothermic in one Direction it will be exothermic in the other direction

Energy transferred from the surroundings by the endothermic reaction is equal to the energy transferred to the surroundings during the exothermic reaction

Question 16

what is le Chateliers principle about temperature

Answer 16

all reaction are exothermic in one direction and endothermic in the other

if you decrease the temperature, the equilibrium will move in the exothermic direction to produce more heat. this means you’ll get more products for the exothermic reactions and fewer products for the endothermic reactions and fewer products for the endothermic reactions

if you rise the temperature, the equilibrium will move in the endothermic direction to try and decrease it. You’ll now got more products for the endothermic reaction and fewer products for the exothermic reaction

Question 17

what is le Chateliers principle about pressure

Answer 17

changing the pressure can affect equilibrium involving gases

if you increase the pressure, the equilibrium tries to reduce it - it moves in the direction where there are fewer molecules of gas

if you decrease the pressure, the equilibrium tries to increase it - it moves in the direction where there are more molecules of gas

Question 18

what is le Chateliers principle about concentration

Answer 18

if you change the concentration of either the reactants or the products, the system is not in equilibrium

so the system responds to bring itself back to equilibrium

if you increase the concentration of the reactants the system tries to decrease it by making more products

if you decrease the concentration of the products the system tries to increase it by making more reactants