3.3 Rates of reaction Flashcards
Collision theory, activation energy, factors affecting rate of reaction
Collision Theory
for a reaction to occur, particles must collide with:
1. Sufficient energy
2. Correct orientation
In order to break existing bonds and to form new bonds
Activation Energy
minimum amount of energy needed for a reaction to occur
Reaction Rate
rate reactants are used up AKA rate products form
6 Factors that affect reaction rate:
- Nature of the reactants
- Surface area and particle size
- Concentration of reactants in solution
- Pressure of any gaseous reactant
- Temperature of the reaction mixture
- Presence of a catalyst
rate of reaction
(1) if reaction requires breaking bonds
(2) if reaction doesn’t require breaking bonds
(1) rate will be slow at room temperature (higher activation energy)
(2) rate will be fast at room temperature (lower activation energy)
increasing surface area or particle size means:
more reactant molecules are exposed to collision
increasing surface area:
(1) solids → powder
(2) liquids → sprays
increasing concentration of reactants
increases chance of particle collision = increases rate of reaction
increasing pressure of gaseous reactants means:
it increases the chance of collisions between particles
*changing pressure doesn’t affect solids or liquids
increasing temperature of the reaction mixture
increases average kinetic energy of reactants = more collisions
*Changes distribution of molecular kinetic energy: more reactants with sufficient kinetic energy to fulfil needed activation energy
what a catalyst is and it’s function
a substance that increases rate of reaction but don’t undergo permanent chemical change
(1) Provides alternative reaction pathway of lower activation energy
(2) Makes it so that bonds can be broken more easily and rebond more easily
Homogeneous catalysts
(1) state
(2) function
(1) same physical state as reactants and products
(2a) catalyst weakens bonds or
(b) molecules react with catalyst surface then are desorbed (broken away)
Heterogeneous catalysts
(1) state
(2) function
(1) different physical state from reactants and products
(2) ADsorption is where molecules sticks to catalyst surface (not ABsorption)
(3) ways of Measuring Reaction Rate
(1) Comparing volume of gas produced over time
(2) Change in colour over time
(3) Mass loss over time
(2) ways to increase pressure of gas
(1) adding more reactant gases to a fixed volume vessel
(2) reducing the volume of the vessel
