Rates
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Define rate of reaction
Concentration of product or reactant/ time
What are the units of rate of reaction?
moles per dm cubed
What is the effect of an increase in concentration on collisions?
Increases the frequency
What is the effect on rate of reaction if particles collide more frequently?
Increases the rate of reaction
What conditions must occur for particles to react?
Particles must collide and have energy which exceeds the activation energy
Why does a higher pressure increase the rate of reaction?
• there are more particles in a given volume • so collisions occur more frequently • more frequent collisions mean a faster rate of reaction
Give 3 ways the rate of reaction can be monitored
• measure loss in mass rate • measure rate of gas produced • measure change in numbers of ions using a conductivity metre • measure colour change • measure change in pH
Why in the second half of a reaction is the rate slower?
Concentration of reactants gets lower so the frequency of collisions between particles decreases as there are fewer particles in a given volume
How do you calculate rate of reaction for time t?
• draw a tangent at time t - calculate the gradient of the line
What is a catalyst?
A substance that increases the rate of a chemical reaction without being used up in the process; a catalyst provides an alternative
What is the effect of a catalyst on the overall enthalpy change of a reaction?
It has no effect on the overall enthalpy change
What is a heterogeneous catalyst?
A catalyst with a different physical state from the reactants
What is a homogeneous catalyst?
A catalyst with the same state as the reactants
Give 2 examples of reactions with heterogeneous catalysts and name the catalysts
1) N2 + 2H2 —-> 2NH3 (Haber process) Iron 2) H2C=CH2 + H2 —–> CH3CH3 Nickel
Give an example of a reaction with a homogeneous catalyst and name the catalyst
CH2=CH2 + H2O —-> CH3CH2OH H3PO4 catalyst
How do catalysts influence energy consumption and the effect of a reaction on the environment?
• Reactions using catalysts require less energy, less electricity, and less fossil fuel is used • less of a resource is used • using less fossil fuel produces fewer pollutants and cuts CO2 emissions which is linked to global warming
How do catalysts affect atom economy and waste of a reaction?
• using a catalyst reduces waste - improves atom economy
What is the economic importance of catalytic processes?
• increases profitability of a reaction because product is made faster and less energy is used • economic advantages of using a catalyst outweigh any costs associated with developing catalytic processes