chemical change

what do ‘big numbers’ in front of formulae tell us

how many units of each formulae there is in the balanced equation

what do ‘small numbers’ in formulae tell us

how many atoms of each kind are in a formulae

what is the law of conservation of mass

atoms are not created or destroyed in a chemical reaction

in the reaction metal + acid ➡ salt + hydrogen, why does the mass decrease?

atoms are being lost as a gas (hydrogen)

in the reaction magnesium + oxygen ➡ magnesium oxide, why does the mass increase?

atoms from a gas (oxygen) are being added

unit and symbol for mass?

kilogram/kg - gram/g

unit and symbol for volume?

cubic metres/m - cubic decimetre

what is concentration

the amount of solute dissolved per unit volume of solvent

unit and symbol for concentration (when using mass)?

grams per cubic decimetre

what must particles do in order to have a chance to react?

collide (with sufficient energy and in the correct orientation)

what is rate of reaction?

how quickly a reaction takes place

units and symbols for rate?

cubic centimetres per second and grams per second

how can you monitor rate of reaction

how quickly a product is formed, or a reactant is used

how can you measure how quickly a product is formed

volume of gas per second using a gas syringe, change in mass

how can you measure how quickly a reactant is used

change in mass

what is turbidity

cloudiness

how can you monitor changes in concentration to measure rate?

changes in colour or turbidity (disappearing cross)

how can you calculate relative rate from time taken

relative rate = 1/time taken

on a graph of concentration/mass/volume of gas against time, what is represented by the gradient

rate of reaction

what are the 5 factors that can alter the rate of reaction

temperature, surface area, pressure (gases), concentration and catalyst

how does temperature affect rate of reaction

increasing temperature increases rate of reaction

what needs to happen to collisions between particles to increase rate

increased frequency and/or increased energy

how do particles behave at higher temperatures?

they move faster and collide more frequently

what do particles have more of at higher temperatures

energy

which state of matter can we alter the pressure of?

gases

how does pressure affect rate of reaction

increasing pressure increases rate of reaction

how are particles spaced at high pressure

closer together - more particles per unit volume

how does concentration affect rate of reaction

increasing concentration increases rate of reaction

how are particles spaced at low concentration

further apart - fewer particles per unit volume

what effect does breaking solid matter into smaller bits have on surface area

increases surface area to volume ratio

how does surface area affect rate of reaction

increasing surface area increases rate of reaction

why does a larger surface area increase rate of reaction

more particles at the surface and available for collisions

what is activation energy

the minimum energy with which particles must collide in order to react