Wk1 - kinetics
Chemical Kinetics Study of the rates (or speeds) of reactions • The “hill” in the energy profile reaction diagram • Small hill = lower barrier ∴ faster reaction • Uses - Industry - Biology - Medicine
Activation Energy Ea
Enthalpy ΔH
Rate Change in concentration of a reaction with time (v) • Rate is always a positive value • Standard Units: molL-1s-1 or pressure.time-1 A —> B
or
• More accurate by considering an infinitely small Δt • By finding the tangent at that point on the curve ∴ calculus is used
Rate and Stoichiometry
The rate of the products disappearing depends can be found using the rate of formation. • These rates must be equal in magnitude - the rate of disappearance for ClO2(g) = 2.4 x 10-3 molL-1s-1 - the rate of disappearance for F2(g) = 1.2 x 10-3 molL-1s-1
The integration process to finds rates shows us that the above is simply asking for the rates of each of those substances
- part i = +2.4 x 10-3 molL-1s-1 - part ii = -1.2 x 10-3 molL-1s-1
Rate of reaction v = d[FClO2]/(2.dt) = 1.2 x 10-3 molL-1s-1
Measuring Reaction Rates Accurately determine the concentration of certain species at particular points in time • taking samples and analysing • titration • spectroscopic continuous monitoring • • spectroscopic methods • electrochemical techniques • measuring gas pressures
Factors that Affect the Reaction Rate AKA affecting properties within the COLLISION THEORY • Reaction = forming and breaking of chemical bonds through collisions • Change the rate/proportions of collisions
Intrinsic Properties 1. Orientation • Species must collide in a certain position to react
2. Activation Barrier • Lowered by a catalyst • It increases the proportion of collisions in the reaction
3. Temperature • Temperature is a measure of the kinetic energy within a particle,which has an effect on its velocity in a system • Increasing the temperature will then cause the kinetic energy to rise and thus the speed of the particles will increase causing a greater proportion of successful reactions • When they collide more likely they will react • Faster in the system thus a greater number of collisions
4. Particle Size • When a reaction involves 2 different phases (heterogeneous reactions) • The surface area of a substance is where the reaction takes place • Larger surface area will have a greater space for collisions to take place thus there is a greater number of collisions thus increasing the rate
5. Concentration • When a reaction involves 1 phase (homogeneous reactions) • An increase in concentration means there are more reactants in proportion to a lower concentration hence the frequency of collisions increase thus the rate increases
• Rate Law Equation:
• It is an experimentally derived equation Rate = k[A]x[B]y
• • • •
k = rate constant x = order of reaction with respect to A y = order of reaction with respect to B x + y = overall order of reaction
Need to find x and y • Cannot just use the chemical equation to derive x and y • To find x —> use 2 experiments where [B] is the same • x=1 • The reaction is first order in respect to A
“if either x or y is zero, the rate is independent of the concentration of that particular reagent”
• Similarly to find y —> use 2 experiments where [A] is the same • y=2 • The reaction is second order in respect to B
Integrated First Order Rate Equation: • Allows concentration to be expressed as time varies
Total concentration of A at any time is = initial concentration of A multiplied by e-kt
Activation Energy Ea
Enthalpy ΔH
Rate Change in concentration of a reaction with time (v) • Rate is always a positive value • Standard Units: molL-1s-1 or pressure.time-1 A —> B
or
• More accurate by considering an infinitely small Δt • By finding the tangent at that point on the curve ∴ calculus is used
Rate and Stoichiometry
The rate of the products disappearing depends can be found using the rate of formation. • These rates must be equal in magnitude - the rate of disappearance for ClO2(g) = 2.4 x 10-3 molL-1s-1 - the rate of disappearance for F2(g) = 1.2 x 10-3 molL-1s-1
The integration process to finds rates shows us that the above is simply asking for the rates of each of those substances
- part i = +2.4 x 10-3 molL-1s-1 - part ii = -1.2 x 10-3 molL-1s-1
Rate of reaction v = d[FClO2]/(2.dt) = 1.2 x 10-3 molL-1s-1
Measuring Reaction Rates Accurately determine the concentration of certain species at particular points in time • taking samples and analysing • titration • spectroscopic continuous monitoring • • spectroscopic methods • electrochemical techniques • measuring gas pressures
Factors that Affect the Reaction Rate AKA affecting properties within the COLLISION THEORY • Reaction = forming and breaking of chemical bonds through collisions • Change the rate/proportions of collisions
Intrinsic Properties 1. Orientation • Species must collide in a certain position to react
2. Activation Barrier • Lowered by a catalyst • It increases the proportion of collisions in the reaction
3. Temperature • Temperature is a measure of the kinetic energy within a particle,which has an effect on its velocity in a system • Increasing the temperature will then cause the kinetic energy to rise and thus the speed of the particles will increase causing a greater proportion of successful reactions • When they collide more likely they will react • Faster in the system thus a greater number of collisions
4. Particle Size • When a reaction involves 2 different phases (heterogeneous reactions) • The surface area of a substance is where the reaction takes place • Larger surface area will have a greater space for collisions to take place thus there is a greater number of collisions thus increasing the rate
5. Concentration • When a reaction involves 1 phase (homogeneous reactions) • An increase in concentration means there are more reactants in proportion to a lower concentration hence the frequency of collisions increase thus the rate increases
• Rate Law Equation:
• It is an experimentally derived equation Rate = k[A]x[B]y
• • • •
k = rate constant x = order of reaction with respect to A y = order of reaction with respect to B x + y = overall order of reaction
Need to find x and y • Cannot just use the chemical equation to derive x and y • To find x —> use 2 experiments where [B] is the same • x=1 • The reaction is first order in respect to A
“if either x or y is zero, the rate is independent of the concentration of that particular reagent”
• Similarly to find y —> use 2 experiments where [A] is the same • y=2 • The reaction is second order in respect to B
Integrated First Order Rate Equation: • Allows concentration to be expressed as time varies
Total concentration of A at any time is = initial concentration of A multiplied by e-kt
