chemical reactions 1.2 NCEA

chemical change

when substances alter into new substances, irreversible

physical change

when the form of a matter is changed, but no new substance, reversible

signs of chemical change

light produced, gas produced, precipitate formed, colour change, heat

example of a chemical change

frying eggs, rusting, burning wood, digestion

signs of physical change

change in size or shape

example of a physical change

crushing a can, breaking glass, ice melting, folding paper

Compounds

pure substance made up of 2 or more atoms chemically combined

reactants

A+B

products

=AB

H2SO4

hydrogen sulfate or sulfuric acid

NH4

ammonium

PO4

phosphate

CO3

carbonate

SO4

sulfate

OH

hydroxide

NO3

nitrate

HCO3

hydrogen carbonate

HCL

hydrochloric acid

mass number

top, not consecutive, protons+neutrons combined

atomic number

bottom, consecutive, no. of protons

protons is equal to

electrons

to find the neutrons

mass number- protons

1st shell

2nd shell

3rd shell

4th shell

2,8,8,18

valence shell and electrons

outer shell and outer electrons that determine reactivity of atom

full valence shell atoms are

stable, not very reactive, neutral

neutral

same number of protons, neutrons and electrons

atoms become ions when

they lose or gain electrons in a chemical reaction

why do atoms lose or gain electrons

to get a full outer shell

metal ions

are positive, called cations and lose electrons

non-metal ions

are negative, called anions and gain electrons

polyatomic ions

atoms stuck together in special groups

conservation of mass

is a principle stating that mass cannot be created nor destroyed during a chemical reaction or physical change, but is always conserved. The total mass of the products must be the total mass of the reactants, the number and type of atoms in a reaction do not change.

all ions have a what

full outer shell

hydroxide is a

base

hydrogen is present in all

acids

why does lime water turn cloudy in the presence of co2?

because they react and form CaCO3, which is insouble, therefore creating the cloudy precipitate

all atoms are

neutral because they have the same number of protons and electrons

opposite charged ions are

attracted to each other

metal + acid =

salt, hydrogen

acid + base =

salt, water

acid + metal carbonate

salt, water, carbon dioxide

combination reaction

a chemical reaction in which 2 or more reactants chemically bond to form a product, A+B=AB

decomposition reaction

a chemical reaction in which a compound breaks down into two or more substances, AB=A+B