Topic 7 - Rates of Reaction and Energy Changes✅

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What are the two core practicals that can be done to test rate of reaction

• Hydrochloric acid and marble chips

• Disappearing cross

Method for marble chips experiment

• Set up a conical flask with hydrochloric acid, a bung, and a gas syringe (supported with a clamp)

• Add 0.4g of marble chips then attach the bung and start a timer

• For every 10cm of gas produced, record the time taken

• Repeat these steps with different concentrations of acid, or sizes of marble chips

What's the equation for this experiment

2HCl(aq) + CaCO₃(s) -> H₂O(l) + CaCl₂(aq) + CO₂(g)

What gas is collected in the gas syringe

Carbon dioxide

Method for disappearing cross experiment

• Set up a conical flask with dilute sodium thiosulfate

• Draw a cross on a piece of paper and put it under the conical flask

• Add dilute hydrochloric acid to the conical flask and start the timer

• Record the initial temperature of the solution

• Stop the timer as soon as the cross is no longer visible

• Repeat steps with different starting temperatures (use a water bath)

What is the equation for this experiment

Na₂S₂O₃(s) + 2HCl(aq) -> 2NACl(aq) + H₂O(l) + SO₂(g) + S(s)

What is the precipitate formed

Sulfur

Explain how reactions occur when particles collide

Reactions occur when particles collide with enough energy

How can you speed up rate of reaction

• You can speed up rate of reaction by increasing the frequency and energy of collisions

• This can be done by:

• increasing pressure,

• temperature,

• concentration,

• surface area,

• using a catalyst

How does changing temp. affect rate of reaction

• Increasing temp increases rate of reaction

• This is because the particles have more kinetic energy

• So they collide more frequently and with more energy

How does changing concentration affect rate of reaction

• Increasing conc. increases rate of reaction

• More particles in a given volume

• Increases frequency of collisions

How does changing surface area affect rate of reaction

• Increasing SA:V ratio increases the rate of reaction

• More areas are exposed for collisions

• Therefore more frequent collisions

How does changing pressure affect rate of reaction

• Increasing pressure increases rate of reaction

• More particles in a given volume

• Therefore more frequent collisions

What is a catalyst

• A substance that speeds up the rate of reaction

• Without altering the products

• Without changing itself chemically / being used up

How do catalysts increase rate of reaction

• Catalysts decrease the activation energy;

• this increases the amount of particles with energy to react,

• leading to more frequent successful collisions and so an increased rate of reaction

• They provide a different pathway for a chemical reaction that has a lower activation energy.

What are enzymes

Biological catalysts

When are enzymes used

In the production of alcoholic drinks

What type of reaction is salts dissolving in water

Exothermic or endothermic

What type of reaction are neutralisations reactions

Exothermic

What type of reaction are displacement reactions

Exothermic or endothermic

What type of reaction are precipitation reactions

Exothermic

How can you measure the temperature change of these reactions when they take place in a solution

When these reactions take place in a solution you must carry them out in a polystyrene cup with a lid Measure the temperature change using a thermometer

What is an exothermic reaction

A reaction where heat is give out

What is an endothermic reaction

A reaction where heat energy is taken in

What type of reaction is the breaking of bonds

Endothermic

What type of reaction is the making of bonds

Exothermic

What makes the overall heat energy change for a reaction exothermic?

heat energy released in forming the bonds in the products is more than energy required in breaking the bonds in the reactants

What makes the overall heat energy change for a reaction endothermic

If the heat energy released in forming the bonds in the products is less than the energy required in breaking the bonds in the reactants

What is activation energy

Activation energy is the minimum amount of energy that particles must have to react