Chemical Reactions

 explain the Law of Conservation of Mass  differentiate between subscripts and coefficients  balance skeleton equations by adding coefficients  move between word equations and chemical reactions

ReactantsProducts CoefficientSubscript Solid stateLiquid state Gas stateAqueous state Law of Conservation of Mass Key Words

subscript Chemical formula - show the type and amount of each atom present in a compound. H HO

H HO H HO H HO H2OH2O3 form 3 molecules of water. 6 atoms of hydrogenand 3 atoms of oxygen

CompoundNumber of particles Total of each element KHCO 3 1 formula unitK – 1 H – 1 C – 1 O – 3 AlCl 3 3 formula unitsAl – 3 Cl – 9 CBr 4 6 moleculesC – 6 Br – 24 H 2 SO 4 5 formula unitsH – 10 S – 5 O – 20 C 11 H 22 O 12 4 moleculesC – 44 H – 88 O – 48

Some covalent compounds can act as ions – these compounds are called polyatomic ions. Polyatomic ions carry a known charge. Cl Na +1

The nitrate ion, NO 3 1-, consists of 1 nitrogen atom and 3 oxygen atoms. These atoms form a covalent group that takes one electron and carries a charge of Na

+1 Na Na(NO 3 ) Mg +2 NO 3 -1 Mg(NO 3 ) 2 1 atom of magnesium, 2 atoms of nitrogen, and 6 atoms of oxygen.

Chemical reaction – substances react to produce one or more new substances. Chemical equation – contains all necessary information about a reaction (like a recipe). reactantsproducts A + 2 B C + 2

H + O H 2 O Chemical reactions can be shown as word equations: Hydrogen gas and oxygen gas react to form water vapour diatomic (g) 22

“aqueous” – compound is dissolved in water. State (phase) of the substance is always shown as small subscripts after the numbers. l = liquid g = gas s = solid aq = aqueous

Coefficients indicate the ratio of the substances in the chemical reaction. Two molecules of hydrogen react with one molecule of oxygen to yield two molecules of water. H 2 (g) + O 2 (g) H 2 O (g) H O HHH O 22 HH O HH O

The Law of Conservation of Mass: In any chemical reaction matter cannot be created or destroyed. Atoms will rearrange to form new compounds, but the number and type of atoms will not change during the reaction.

1000 kg

H 2 (g) + O 2 (g) H 2 O (g) 22 Coefficients subscripts (phase/state) reactantsproducts In any chemical reaction matter cannot be created or destroyed.