Reactions

rate of reaction

rate of reaction = amount of reactant used or product formed ÷ time taken
to measure amount of reactant used;
- if 1 product is a gas, measure mass in grams of reaction mixture before&after
- measure the time it takes for reaction to happen
- mass of mixture will decrease
- units for rate of reaction given as g/s
to measure amount of products formed;
- if product is a gas, measure its volume w/ gas syringe in cm³ & time it takes
- units for rate of reaction given as cm³/s
to measure time it takes for reaction mixture to go opaque/change colour;
- time how long it takes to go opaque/change colour
- rate of reaction = 1 ÷time taken to change colour

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chemical reactions happen b/c particles collide with each other with sufficient energy
minimum of energy needed to cause reaction is called activation energy
4 factors affect rate of reaction: temp, concentration, surface area, catalysts
temperature;
- in hot reaction mixture, particles move more quickly - collide more often with more energy - so more successful collisions
Concentration;
- at high concentration, particles are crowded closer together - collide more - so more successful collisions
- PRESSURE also has effect
Surface area;
- small pieces of solid reactant have big surface area compared to volume
- more of their particles exposed & available for collisions - so more collisions & faster reaction
to find rate of reaction at particular time on graph; draw tangent to curve at that exact time, find gradient of tangent

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in closed system: no reactants added & no products removed
if reversible reaction is in a closed system - equilibrium is achieved when:
- rate of forward reaction = rate of backward reaction
Exothermic;
- temperature increases - equilibrium shifts to left so more reactant formed
- temperature decreases - equilibrium shifts to right so more product formed
Endothermic;
- temperature decreases - equilibrium shifts to left so more reactant formed
- temperature increases - equilibrium shifts to right so more product formed
pressure increases; equilibrium shifts to side with less moles (least number of gas molecules)
pressure decreases; equilibrium shifts to side with more moles (most number of gas molecules)
if concentration of reactant increased; equilibrium shifts so more products formed until its equilibrium again
if concentration of reactant decreases; equilibrium shifts for more reactants are formed until its equilibrium again

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