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As the concentration of H₂O₂ increases, the rate also increase. It is directly proportional, first order process.

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1 ÷ t = rate (s⁻¹)

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Planning - decide on the volumes of H₂O₂ solution & water you mix together to get 4 different concentrations of H₂O₂. Each test requires:

1cm³ starch solution

10cm³ H2SO4 solution

10cm³ sodium thiosulpahte

25cm³ KI solution

Total volume must be 50cm³.
General method -

1. In separate conical flasks, make up solutions according to your concentration values(table) & the other chemicals. Don't add peroxide at this stage.

2. Mix thoroughly

3. Rapidly add the hydrogen peroxide to the test flask, starting the stop watch immediately after

4. Swirl to mix the reaction mixture thoroughly

5. Stop timing when the solutions turns blue-black & record the time

6. Repeat the experiment for the other test flasks

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We use colorimetry to track the rate of reaction where there is a colour change.

CH₃COCH₂ + I2 --> CH₃COCH₂I+ HI
Measure the intensity of the iodine - colorimeter. Rate of disappearance of iodine can be track/measured.

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Homogeneous Catalysts

Reactants and catalyst are in the same state

Eg. A reaction in solution where the catalyst is a metal ion dissolved in water

Heterogeneous Catalysts

Reactants and catalysts are in different states

Eg. Reactions between gases that are catalysed on a solid metal surface

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For a certain reaction, increasing the temperature by 10 degrees roughly doubles the number of particles with E>EA

Increasing Temperature

Make particles collide more frequently ( small increase in rate)

Makes it more likely that collisions will cause a reaction  (more effective collisions) (large increase in rate)

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Shows us how energy is distributed amongst particles in a certain system

Shows our system as it is at a set temperature.

The curve we see is called a Boltzmann Distribution

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A catalyst is a substance that speeds up a chemical reaction.

At the end of the reaction, the catalyst remains unchanged.

Catalysts increase reaction rates by providing alternative routes of lower activation energy.

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Activation energy, EA , is the energy needed to start off a reaction

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Relationships between concentration and rate

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Relationships between concentration and rate

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When the concentration of reagant X doubles, there are a number of possible effects on this rate:
Rate unchanged- rate not dependant on X
Rate doubles - rate proportional to [X]
Rate goes up by a factor of 4 - rate proportional to [X]²

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Slope at t = Δ[products] ÷ Δt
Rate at time, t = slope of tangent at t
Units = moldm⁻³s⁻¹

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To measure the rate, we need a physical or chemical quantity that varies with time.

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1. Increasing temp. gives higher energies to particles & more effective collisions between them(& more often)

2. Increasing conc. of a reactant gives more particles & more collisions

3. For gases, increasing pressure can restrict particles to a smaller volume to give more particles. The number of collisions will increase

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The more collisions between particles in a certain time, the faster the reaction.

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Surface area (of solid reactants)

Concentration (of reactants in solution)

Pressure (of gaseous reactants)

Temperature

Catalysis - adding a catalyst

Light (in some cases)