Kinetics Flashcards
What are the conditions for a collision to result in a reaction?
Correct reactant particles, correct orientation, sufficient energy
5 factors that affect rate of reaction
Temperature, pressure, catalyst, concentration of solutions, surface area/particle size
How increasing temp increases rate of reaction
Particles have more kinetic energy -> collide more frequently and each collision occurs with greater energy therefore greater proportion of collisions occur with required activation energy. More successful collisions.
How increasing concentration increases rate of reaction
More reactant particles in given volume of solution. increases freq of collisions which increases successful collisions.
Surface area increasing/particle size decreasing increases rate of reaction
For same mass of solid, smaller particles means more exposed reactant particles, increases freq of collisions between reactant particles which increases freq of successful collisions.
How does catalyst increase rate of reaction
Provides alternative route for reaction with lower activation energy. Greater proportion of collisions will occur with required activation energy, increases successful collisions. CATALYST IS CHEMICALLY UNCHANGED.
What is Ea
Activation energy: minimum energy which a collision between reactants requires for reaction to occur and products to be formed.
How to find rate of reaction and units when no mass/volume given
rate of reaction = 1 / time taken for reaction to complete
How to find rate of reaction with mass/volume
Amount of reactant / time taken
How to work out reaction rate from graph
draw tangent
Heterogenous catalyst
Different phase from reactants. Happens on surface of catalyst therefore increasing surface area of catalyst increases rate of reaction. Lowers activation energy
Homogenous catalyst
Same phase as reactants. Normally aqueous among aqueous reactants. Reactants combine with the catalyst to make intermediate species which then forms product.
What is Maxwell-Boltzmann distribution
Curve that shows few molecules move slowly, most molecules move at moderate speed and few molecules have over Ea.
Industrial uses of catalyst
Lower production cost (less harsh environment making product), more product and better properties of product.
How to draw Maxwell-Boltzmann curve
Draw normal distribution and then skew it left. When raising temp, lower the peak to the right and make the gradient smaller.
Rate equation
Rate = k [A]^order * [B]^order
What does 0 order mean in rate equation
Does not feature or affect rate.
How to find overall order of reaction
Sum of all orders
What is the rate constant dependent on?
Temperature
What does a constant half life for concentration of reactant mean for order?
1st order
What does a straight line for concentration of reactant mean for order?
0 order
What is the slow step in the reaction?
Step that takes the slowest, RDS, all reactants in rate equation involved before or during it.
How to obtain rate of reaction: titration
Take regular samples during reaction and quench. Measure conc. of reactants by titration.
How to obtain rate of reaction: colorimetry
Tracks concentration of specific species with distinct colour. Amount of light absorbed proportional to the conc. of reactant.
How to obtain rate of reaction: mass change
Can be used to measure mass of reaction when a gas is produced.
How to obtain rate of reaction: volume of gas evolved
Measure volume of gas produced via gas syringe or collection over water
Rate equation for SN1
Rate = k [Haloalkane]
Rate equation for SN2
Rate = k [Haloalkane] [Nu:]
When is SN1 fastest
When the carbocation intermediate is the most stable as it makes the slow step faster directly.
Iodine clock reaction H2O2 + 2I- + 2H+ -> 2H2O + I2
Small amount of sodium thiosulfate solution and starch added to excess H2O2 and iodide ions in acid solution.
Any iodine that forms reactions with thiosulfate. When all thiosulfate reacted, mixture will turn blue-black as iodine in solution gone.
Time taken for reaction to occur and conc of reactants can give initial rate w.r.t reactant.
0 order conc to time; rate to conc. of reactant shape
Constant gradient; horizontal line
1 order conc to time; rate to conc. of reactant shape
Downwards curve constant half life; increasing rate with constant gradient
2 order conc to time; rate to conc. of reactant shape
Downward curve, not constant half life; increasing rate with increasing gradient, but if plotted against conc. squared then constant gradient.
Gradient of graph of ln(k) plotted against 1/T
-Ea / R in joules/mol
