c5 - monitoring + controlling chemical reactions

doesn't include flame tests

what is chatelier’s principle?

if there is a change in concentration, pressure or temperature in a reversible reaction, the equilibrium position will move to counteract that change

what happens to equilibrium when you increase temperature

equilibrium will shift to the endothermic side to absorb extra heat

what happens when you increase pressure

equilibrium shifts to the side with fewer moles of gas to reduce pressure

what happens when you increase concentration of the reactants

equilibrium will shift to the right to use up the reactants, making more products

what happens when you increase concentration of the products

equilibrium will shift to the left to use up the products, making more reactants

what is a reversible reaction

a reaction where the products can react and change back to the original reactions

what does it mean if the equilibrium lies to the right

lots of the products and not much of the reactants

what is a closed system

none of the reactants or products can escape, a closed system is necessary to reach equilibrium

what is dynamic equilibrium

the concentration of reactants and products have reached a balance and won’t change, though both reactions will still be happening

how is equilibrium reached

as reactants react, their concentration falls so the forward reaction will slow down. as products are made, their concentration will rise so the backwards reaction will speed up.

what is a catalyst

a substance that increases the rate of reaction without being used up

how do catalysts work

they decrease the activation energy by providing an alternative reaction pathway

what are enzymes

biological catalysts

how can you identify a catalyst

by measuring the rate of reaction with and without the catalyst present while keeping volume, temperature and concentration constant

what is the formula to calculate relative rate of reaction

1 / time

how do you find the rate of reaction from a graph

by finding the gradient of the tangent to the curve

what 2 things do the rate of reaction depend on

collision frequency and energy transferred (particles must reach the activation energy for the reaction to be successful)

how does increasing the temperature affect rate of reaction (3 points)

particles move faster leading to more collisions

energy increases meaning more particles reach the activation energy

there are therefore more frequent successful collisions, increasing rate of reaction

how does increasing the concentration / pressure affect rate of reaction

there are more particles in the same area as they are more crowded meaning more frequent successful collisions, increasing rate of reaction

how does increasing the surface area affect rate of reaction

surface area to volume ratio increases so there is more area to reacting meaning more frequent successful reactions, increasing rate of reaction

what reaction can you use to measure the effect of concentration on the rate of reaction

reacting magnesium with different concentrations of hydrochloric acid. it produces hydrogen so you can measure the change in mass using a scale.

what reaction can you use to measure the effect of surface area on the rate of reaction

reacting different sized marble chips with hydrochloric acid and measuring the volume of hydrogen gas produced using a gas syringe

rate of reaction formula

rate of reaction = volume of reactants used or products formed / time

how can you measure rate of reaction in precipitation reactions

by timing how long it takes for a cross drawn under the beaker to disappear after mixing the reactants together

what does the atom economy tell you

what percentage of the mass of the reactants has been converted to the desired product

what is the theoretical yield

the mass of products you’d make if all the reactants were converted

what is the molar volume

the volume occupied by one mole of gas which is 24dm³ at room temperature and pressure

molar volume formula

molar volume = gas volume / number of moles

how do you perform a titration

measure a set volume of alkali into a conical flask using a pipette

add an indicator with a sudden change

drip acid into the flask using a burette while swirling the flask

when the indicator changes colour the alkali has been neutralised

record the volume of acid used (the titre)

repeat to find the mean from concordant results

what indicator can you use for titration

phenolphtalein which is pink in alkalis and colourless in neutral solutions

concentration equation

concentration = number of moles / volume of solution

concentration = mass of solute / volume of solution