Speed of reaction Flashcards
Rate of reaction
the increase in the conc of one of the products per unit time or as the decrease in the conc of one of the reactants per unit time
SI Unit: mol dm-3 s-1
Colour change test
Use colorimeter to determine change in intensity of colour over time (eg. zinc displace copper sulfate, mixture goes from blue to colourless)
pH change test
acid-alkali reactions
remove samples at regular intervals during the experiment and conduct titration to calculate the amount of acid/alkali left
Collision theory
For a reaction to occur
1. particles must collide
2. particles must possess sufficient kinetic energy to overcome the activation energy of the reaction
3. particles must collide in the correct orientation such that the reactive parts of the particles/molecules come into contact
Pressure effect on rate of reaction
When pressure increases for GASEOUS reactants, the number of reacting particles per unit volume increases. Hence the number of collisions between particles increase and the frequency of effective collisions also increase
Particle size effect on rate of reaction
For solids, only particles on the surface of the reactant can come into contact with surrounding reacting particles and react
When particle size decreases, the total exposed surface area of the reactant increases, allowing for an increased number of collisions and an increase in the frequency of effective collisions
For extra finely divided powders, rate of reaction is extra high (explosive/violent reaction)
Why rate of reaction graph become less steep
Why rate of reaction graph go flat
As the reaction progresses, the concentration of reactants in the mixture decreases
All of the limiting reactant has been used up and the reaction is complete
What are catalysts
Transition metals and their compounds
Why industrial catalysts are good despite being expensive
- They speed up the rate of reaction such that industrial processes can be completed in a shorter amount of time, using less fuel
- They remain chemically unchanged at the end of the reaction (they can be reused and purchasing them is a one time cost)
What is a catalyst
substance that increases the rate of reaction but itself remains unchanged quantitaviely and chemically
provides an alternative reation parthway with a lower Ea
Catalyst effect on rate of reaction
Catalysts provide an alternative reaction pathway with lower activation energy. Hence a larger fraction of reacting particles will have sufficient kinetic energy to overcome the new lower activation energy which increases the frequency of effective collisions
Temperature effect on rate of reaction
As temperature increases, the kinetic energy of reaction particles increase and the number of reacting particles with kinetic energy equal or greater than the activation energy increases significantly. Hence the frequency of effective collisions between reacting particles increase, increasing rate of reaction
Concentration effect on rate of reaction
As concentration increases, the number of reacting particles per unit volume increases, increasing the number of collisions and frequency of effective collisions hence increasing rate of reaction
