U3AOS2 - Rate of Chemical Reactions Flashcards
Collision Theory requirements
- the reactants must actually collide
- they must collide with sufficient energy to overcome Ea
- they must collide with the correct orientation to break the bonds within the reactants
Maxwell-Boltzmann Curves
Represents the range of kinetic energies of particles in a reaction, and shows the proportion of particles that can overcome the activation energy barrier
Y Axis Intercepts on Maxwell-Boltzmann Curves
Cannot be 0, as no particles have a kinetic energy of 0 (unless at 0K)
What is the effect of temperature on Maxwell-Boltzmann Curves
increasing temperature increases the average kinetic energy, flatting the curve, and increasing the proportion of molecules that can overcome Ea
What is the effect of catalysts on Maxwell-Boltzmann Curves
modifies the Ea position, the curve will stay the same
Exothermic Reaction (inc. energy profile diagrams)
When the total energy of the products is less than the total energy of the reactants
Energy is lost to the surroundings during the reaction
Negative DeltaH
Endothermic Reaction (inc. energy profile diagrams)
When the total energy of the reactants is less than the total energy of the products
Energy is absorbed by the reaction
Positive DeltaH
Effect of Temperature on Rate of Reaction
Increasing temperature increases kinetic energy -> increasing rate of reaction
reasons:
- higher frequency of collisions (due to an increase in KE), in a unit of time
- given there is a greater level of kinetic energy, there will be a higher proportion of collisions with enough energy to overcome Ea
Effect of Surface Area on Rate of Reaction
increasing surface area increases the chance that reactant molecules could collide - increasing frequency of collisions (and thus successful collisions)
2x ways to increase surface area of substances
- crushing the substance
- stirring a solution (will agitate the particles in the solution - which increases surface area)
Effect of Concentration on Rate of Reaction
increasing concentration increases the chance of a collision in solution, thus, increasing rate of reaction
Effect of Gas Pressure on Rate of Reaction
increasing pressure increases the chance of a collision in the system, thus, increasing rate of reaction
remember that pressure can be related through PV=nRT, so ensure that pressure is actually modified (i.e. temperature doesn’t remain constant)
Effect of an Inert Gas on Gas Pressure
Will increase the pressure – there will be more collisions
Effect of Catalysts on Rate of Reaction
catalysts provide an alternate reaction pathway with lower activation energy,
thus - the rate of reaction will increase as there will be a greater proportion of successful collisions within a unit of time (however - will have no impact on number of collisions as KE hasn’t changed)
4x ways to measure rate of reaction
- observe change in pH
- observe rate of color change over time
- if reaction produces a precipitate - measuring the mass of the precipitate
- if reaction produces a gas - measure the rate of gas production by collecting gas in cylinder and recording the change in volume over time
Representing Catalysts on Energy Profile Diagrams
Modify the activation energy, but not the overall ΔH
Representing Catalysts on Maxwell-Boltzmann Curves
Modify the location of the Ea, but not the shape or location of the overall curve
