Chp 4 Rates of Chemical Reactions Flashcards
Rate of reaction
The change in concentration of any one reactant or product per unit time
Collision theory
- Collide
- With correct reaction geometry
- Have the activation energy
Activation energy (Eᴀ)
The minimum energy colliding particles require to have a successful collision hence successful reaction
Breaking bonds
Require energy
Forming bonds
Releases energy
Exothermic reaction
Energy is released in the form of light and heat
Endothermic reaction
Reactants absorbs heat energy from surroundings to form products
Allotropes
Different physical forms of the same elements
Factors affecting rate of reaction:
Catalyst
A substance which changes the rate of a reaction without being consumed in the reaction,
Provides an alternate reaction pathway that has a lower activation energy.
Homogeneous catalysis
A homogeneous catalyst is in the same phase as the reactants. (Physical State)
E.g. Iodine snake
Hydrogen preoxide –> water and oxygen
Addition of aqueous iodide ion as catalyst
Spectator ions
Ions which do not take part in a reaction
Heterogeneous catalysis
A heterogeneous catalyst is in a different phase than the reactants
Reduction of Ethene
C₂H₄ + H₂ -> C₂H₆
Catalysed by Ni
Autocatalysis
One of the products of the reaction acts as a catalyst for the reaction
Potassium permanganate and ethanedioic acid forms Magnesium which acts as a catalyst
Negative catalyst (inhibitor)
Slows down a reaction
Catalytic poison
Destroys the effect of a catalyst
Lead poisons the catalyst in a catalytic converter
Adsorption
Reactants diffuses onto surface of catalyst. bonds weakened when adsorbed
Concentration weaken as reactants are clumped together
Absorption
Contact throughout an object
Enzyme
Biological catalyst
Catalytic converter
A device in car exhaust, containing a catalyst to convert pollutant gas into less harmful ones
Dust explosion
If a massive surface area of dust is ignited, a huge sudden release of energy can occur.
If happens in a confined space a dust explosion will occur.
Instantaneous rate of reaction
Rate of reaction at a certain time
Found using line of best fit in graph
Factors affecting rate of reaction:
Nature of reactants
(Covalent substance)
Reacts slower - Bonds have to be broken
Factors affecting rate of reaction:
Nature of reactants
(Ionic substance)
Reacts faster - Ionic solution in aqueous solution are already dissolved in water
Factors affecting rate of reaction:
Particle size
Larger surface area for collisions
Factors affecting rate of reaction:
Concentration
More collisions between reactant particles
Factors affecting rate of reaction:
Temperature
Higher temperature, greater rate of reaction
Increase activation energy of particles so effective collision can occur
Factors affecting rate of reaction:
Presence of solvent
Particles in solution are freer to move around and collide with each other
Factors affecting rate of reaction:
Pressure
Only occurs in gas
Increase in pressure = increase concentration of gas
The surface adsorption theory
Adsorption -> Reaction -> Desorption
Generally heterogenous catalysis
The unstable intermediate theory
One of the reactants combines with the catalyst and forms an unstable intermediate
Generally homogeneous catalysis
Examples of catalytic converter
Ceramic honeycomb coated with platinum, palladium and rhodium catalysts
Carbon monoxide -> Carbon dioxide
Nitrogen monoxide -> Nitrogen
Hydrocarbons -> Carbon dioxide and water
