Studied by 2 people
compound
when two or more elements are chemically combined.
element
when two of the same atoms join together.
molecules
when two DIFFERENT atoms join together.
why do elements join?
to become stable + achieve full outer shell.
ionic compounds
the transferring of electrons between a chemical compound.
what type of substances are ionic compounds between?
metals and nonmetals
covalent compounds
the sharing of electrons between a chemical compound.
what type of substances are covalent compounds between?
non-metals
polyatomic elements
when a lot of atoms join (e.g. sulphate, hydroxide, carbonate, phosphate etc.)
pH scale
ranges from 1-14, with 7 being in the middle/neutral. as you go down, the acidity increases.
base
anything with OH (hydroxide) ions.
indicators used to test the acidity or alkalinity of a substance:
litmus paper
universal indicator
using a pH probe
characteristics of acids:
taste sour
need to be dissolved in water in order to act as an acid
have a pH value less than 7
are very soluble in water
changes the colour of indicators
contain hydrogen atoms that form H+ ions when acid is dissolved in water.
characteristics of bases
tastes bitter
pH ranges from 8-14
soapy to touch
releases hydroxide ions
conducts electricity
changes the colour of indicators
physical changes
change in the physical structure only, not chemically. no new product/substance has been formed. most of the physical changes can be reversed (e.g. the states of matter with water).
chemical change
change in the chemical composition/structure. generally irreversible and forms new product(s) (e.g. burning paper which turns into ash).
law of conservation of mass
mass cannot be created or destroyed, only transferred. Mass of reactants also needs to equal to mass of products.
exothermic reaction
a reaction or process that gives off heat.
endothermic reaction
a reaction or process that takes in thermal energy from its environment to either make or break the chemical bonds between atoms.
activation energy
minimum energy required to start a chemical reaction.
decomposition reaction
anything breaking/decomposing (corrosion, rusting)
equation is below:
AB —> A + B
combination reaction
anything combining
A + B —> AB (e.g. H2 + O2 = 2H2O)
H2SO4
sulphuric acid
HNO3
nitric acid
HCl
hydrochloric acid
CH3COOH
acetic acid
NaOH
sodium hydroxide
NH4OH
ammonium hydroxide
acid + metal reaction (or redox reaction but you don’t need to know that)
a salt + hydrogen
acid + base reaction (neutralisation reaction)
a salt + water
carbonates are normally what?
normally metals
acid + metal carbonates reaction
carbon dioxide + a salt + water
combustion reaction
anything being burned basically (but it will have oxygen and will produce carbon dioxide and water) so it’s fuel + O2 —> CO2 + H2O
test for hydrogen and explain
pop test - where if fire is put over the top of a test tube and it produces a distinctive ‘pop’ sound, that means that hydrogen is present.
test for carbon dioxide and explain
lime water test which involves air being funnelled into lime water and if the lime water turns into a milky white colour, then the gas is carbon dioxide.
indicator that there is hydrogen present?
when there is a distinctive “pop” sound
indicator that there is carbon dioxide present?
when the lime water turns into a milky white colour
precipitation reaction
when two clear solutions are mixed together, the formation of a solid is called a precipitation reaction. the formula is aqueous + aqueous —> solid (or precipitate) + aqueous
rate of reaction
the time taken for a reaction to occur
factors affecting rate of reaction
temperature/heat
surface area
catalysts
concentration of substance
Note 
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