Rates of reaction

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19 Terms

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Rate of reaction

Change in concentration of a reactant or product in a given time

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Rates of reaction are affected by?

Concentration

Temperature

Surface area

Particle size

Catalyst

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Define Collision theory

Reactions occur when reactant particles collide provided that they collide with a certain minimum kinetic energy, the activation energy

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Does orientation matter

Yes, particles must collide with the correct orientation for a reaction to take place

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What are some ways catalysts can interact with a reaction

May react to form an intermediate

It is later regenerated

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What does a catalyst do

A catalyst lowers the activation energy of a reaction by providing an alternative route for the reaction with lower activation energy

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Define a Heterogeneous catalyst

A catalyst that is in a different physical state to the reactants

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Define a Homogeneous catalyst

The catalyst and reactant are in the same physical state

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How does a heterogeneous catalyst work?

reactants absorbed onto surface of the catalyst and the reaction takes place then the products that are formed de absorb and diffuse away

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What is the Boltzmann distribution

shows the no. of molecules with a particular energy, at one temp, often shown as a graph

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Important features of the Boltzmann graph

Area under the curve = total no. of molecules

• No molecules have ZERO energy (curve starts at origin or 0,0)

• No MAXIMUM energy (curve not get to 0 on x-axis)

• ONLY molecules with energy greater than Ea can react

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How would a catalyst effect the Boltzmann distribution

The Ea is lowered so a greater number of particles have greater energy than the Ea so an increased rate of reaction

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Define Dynamic equilibrium

dynamic equilibrium is the equilibrium in a closed system when the rate of forward reaction = rate of reverse reaction

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What are the characteristics of dynamic equilibrium

The concentrations of the reactants and products

do not change over time.

– rate of forward reaction = rate of reverse reaction

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Le Chatelier’s principle

• When a system in dynamic equilibrium is subjected to change, the position of equilibrium will shift to minimise the change.

• Can alter position of equilibrium by changing: – Concs, pressure (gases) or temp

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What are the effects of altering concentrations on equilibrium

Increasing concn of reactants causes ≡m to move to product side.

Increasing concn of products causes ≡m to move to reactants side.

Decreasing concn of reactants causes ≡m to move to reactant side.

Decreasing concn of products causes ≡m to move to product side.

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What are the effects of pressure on equilibrium

Low pressure it moves towards the side with the most number of moles

High pressure it moves to the side with least number of moles

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Effect of temperature on equilibrium

Increase in temperature leads to equilibrium shifting to the lhs as it favours the endothermic reaction

Decreasing the temperature will lead to equilibrium shifting to the rhs as it favours the exothermic reaction

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Whats the equilirium constant

Kc=Conc of products multiplied/Conc of reactants multiplied (Make sure to check units)