CHEMISTRY chemical change (spring)

what do “big numbers” in front of formulae tell us?

how many units of each formula there is in the balanced equations

what do “small numbers” in formulae tell us?

how many atoms of each kind are in a formula

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 incease?

atoms from a gas (oxygen) are being added

unit and symbol for mass?

kilogram/kg (gram/g)

unit and symbol for volume?

cubic metres/m³ (cubic centimetres/cm³) (cubic decimetre/ dm³)

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 - g/dm³

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

unit and symbols for rate?

cubic centimetres per second (cm³/s) and grams per second (g/s)

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 takenon

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 a higher temperature?

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

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