Topic A4 - Kinetics 1
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What is activation energy?
heat energy required (per mole) for a collision between 2 particles to result in a chemical reaction
How does increasing surface area of a solid increase rate?
(rate is proportional to solid surface area) -more solid particles are accessible for collisions -collision frequency increases -successful collision frequency increases
How does increasing solution concentration/ gas pressure increase rate?
-more particles per unit volume -collision frequency increases -successful collision frequency increases
How does increasing temperature increase rate?
-particles have more kinetic energy so move faster -collision frequency increases -larger fraction of collisions have energy greater than activation energy -successful collision frequency increases
How does a catalyst increase rate?
-provides an alternative route with a lower activation energy -large fraction of collisions have energy greater than activation energy -successful collision frequency increases
How do you calculate rate from a curve?
draw a tangent to point of interest
How do you work out average rate, using a curve?
total y-axis change / time
Give 3 discrete ways of measuring rate of this reaction: thiosulfate + acid
-time taken for bubbles to stop being produced -indicator colour change -disappearing cross (S)
Give 3 continuous ways of measuring rate of this reaction: thiosulfate + acid
-pH change, using pH probes (pH would increase) -volume of sulphur dioxide produced (would increase) -conductivity change (would decrease)
What is the distribution of energies in a collection of particles called?
Maxwell-Boltzmann distribution
What does the area under the curve of a Maxwell-Boltzamann distribution mean?
total number of particles
At a higher temperature, how does this effect the Maxwell-Boltzmann distribution?
-peak is further right -peak is lower -graph drops slower (area under graph at energy greater than activation energy is bigger)
With the addition of a catalyst, how does this effect the Maxwell-Boltzmann distribution?
area under the curve at energy greater than activation energy with a catalyst is bigger (no shift in curve peak, just shift in activation energy)
Give 2 ways in which the progress of a reaction can be followed
• monitoring the removal (decrease in concentration) of a reactant • monitoring the formation (increase in concentration) of the product
Give 2 ways in which a reaction that produces gases can be monitored
• monitor volume of gas produced at regular time intervals, using gas collection • monitor the loss of mass of reactants using a balance (both proportional to change in conc of reactant or product)
Heterogenous catalyst =
different physical state from reactants
How do reactants interact with heterogenous (usually solid) catalysts?
• reactant molecules are adsorbed (weakly bonded) onto surface of catalyst • this is where reaction takes place • after reaction, product molecules leave surface of catalyst by desorption
Give 3 features of a catalyst
• it is not used up in chemical reaction • may react with reactant to form intermediate or may provide a surface on which reaction can take place • regenerated at end of reaction
Homogenous catalyst =
same physical state as reactant
How do reactants interact with homogenous catalyst?
form an intermediate - intermediate then breaks down to give product and regenerates the catalyst