MODULE 3: Reaction Rates and Equilibrium
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What is the equation for rate of reaction?
rate = change in concentration/time
What are the factors that can effect rate of reaction?
Concentration, pressure, temperature, catalyst and surface area
What is collision theory?
Theory that states that particles must collide in order for a reaction to occur
What factors effect collision theory?
Orientation of molecules, temperature, catalysts, concentration
What is a catalyst?
A substance that decreases the activation energy by providing an alternative route; therefore increases rate of reaction (does not alter own chemical makeup)
What is a homogenous catalyst?
A catalyst that is the same physical state as the reactants
What is a heterogenous catalyst?
A catalyst that is a different physical state as the reactants
Name an example of a homogeneous catalyst
Ozone depletion (chlorine radicals as catalysts) 2O₃ ⇌ 3O₂
Name an example of a heterogeneous catalyst
Haber process (iron as catalyst) N₂ + 3H₂ ⇌ 2NH₃
What are the benefits of using a catalyst?
Lower activation energy (therefore lower temperature and so less fuel used), less carbon dioxide produced
What is a Boltzmann distribution graph?
A graph to show the spread of molecular energies in gases
What are some of the features of the Boltzmann distribution graph?
Curve starts at origin, no maximum energy, curve stays above zero (area under graph = number of molecules)
How does temperature effect the shape of the Boltzmann distribution graph?
Area shifts to the right, lower peak, greater proportion of successful collisions that leads to a reaction
How does a catalyst effect the shape of the Boltzmann distribution graph?
Provides an alternate route; so lowers activation energy, proportion of molecules have an energy equal or greater than original activation energy
What is equilibrium (dynamic equilibrium)?
When, in a closed, reversible reaction, the reaction rate of the forwards and backwards reaction is the same (concentrations of products and reactants do not change)
What is le Chatelier’s principal?
When a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
What factors can effect a system in equilibrium?
Temperature, pressure and concentration
Why can’t catalyst effect a system in equilibrium?
Because catalysts speed up the rate that each reaction is going, so therefore only reaches equilibrium faster
How does changing the concentration effect a system in equilibrium?
Increasing concentration of reactants on the left decreases concentration of products on the right (and vice versa)
How does changing the temperature effect a system in equilibrium?
If forwards reaction exothermic: shifts left If forwards reaction endothermic: shifts right
How does changing the pressure effect a system in equilibrium?
Increasing pressure increases volume of side with less number of moles of gas
What is the equation for equilibrium law?
Kc = [C]ᶜ[D]ᵈ/[A]ᵃ[B]ᵇ (products/reactants, superscripted letters is moles of)
What does equilibrium law teach us?
Kc = 1: position of equilibrium is halfway between products and reactants Kc > 1: position of equilibrium is towards products Kc < 1: position of equilibrium is towards reactants