Topic 16: Kinetics II 2️⃣
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What are some of the possible methods of measuring the rate of reaction?
Measuring vol of gas produced Measuring change in mass of a reaction mixture Monitoring a colour change (colourimetry) Measuring the change in conc of reactant/product using titration Measuring change in pH of a solution Measuring the change in electrical conductivity of a reaction mixture
Give the rate equation for a first order reaction
rate = k[A]
Give the rate equation of a second order reaction
rate = k[A]^2
Give the rate equation of a 0 order reaction
rate = k
What is the rate determining step
The slowest step in the mechanism for a reaction which determines the spreads at which the overall reaction proceeds
How can you deduce the slowest step from the rate equation
The rate equation only contains species involved in the rate determining step
If something appears in the rate equation but is not in the reaction mechanism, it must be a…
Catalyst
What shape of a conc-time graph indicates a 0 order reaction ?
Negative gradient RoR does not change
What shape of a conc-time graph indicates a 1st order reaction ?
Downward curve RoR slows
What shape of a conc-time graph indicates a 2nd order reaction ?
Steeper downward curve
How do you calculate k for a 0 order reaction using the conc-time graph
Calculate the gradient of the line
How do you calculate k for a 1st order reaction using a conc-time graph
Draw a tangent at a given concentration Calculate the gradient of that line to get the rate Substitute the 2 values into the rate equation to find k
How can half life be used to determine the order of a reaction from conc-time graphs
1st order reactions - half life is constant 2nd order reactions - half life increases
Describe the shape of a rate-conc graph for a 0 order reaction How would you find k from this graph ?
Flat line Y-intercept gives the value of K
Describe the shape of a rate-conc graph for a 1st order reaction How would you find k from the graph ?
Positive correlation line (upwards diagonal) Gradient of line gives us k
Describe the shape of a rate-conc graph for a 2nd order reaction How would you find k from this graph ?
Upwards curve To calc k you would need to plot a second graph (rate vs conc^2) and then the gradient would be k
What does the Arrhenius equation show us
How the rate constant (k) and temperature (T) are related exponentially
Explain how the Arrhenius equation is used graphically
.Ea. 1. ln K = —- —- + lnA .RT. T y =. m. x + c lnA = y intercept Ea= activation energy T = temp in kelvin R= gas constant
What are the two types of mechanisms for nucleophilic substitution reactions
SN1 and SN2
What does an SN1 reaction entail
Only 1 molecule involved in the rate determining step Used in the hydrolysis of tertiary halogenoalkanes 2 step reaction Intermediate formed
What does an SN2 reaction entail
2 molecules involved in the rate determining step Used in the hydrolysis primary halogenoalkanes End up with a transition state