Chemical Reactions G.Burgess 2006

Chemical Reactions Occur when atoms of substances join other atoms of other substances to form different chemical materials There are several types of chemical reactions Chemists show chemical reactions symbolically as chemical equations

Chemical Equations NaOH (aq) + HCl (aq) NaCl (aq) + H 2 O(l) Reactants Products Molecular formula of compound State (aq) = aqueous/ in water (l) = liquid **the ‘+’’s means “reacts with” **the arrow between the reactants and products means “to give”.

Types of chemical reactions 1.Formation(synthesis): when two pure substances combine to make a new substance ie. 2H 2 + O 2 2H 2 O 2.Decomposition: when a compound breaks up into its individual parts. ie. 2H 2 O 2H 2 + O 2

Types of chemical reactions 3.Single displacement: when one element is removed from a molecule and replaced by another element. ie. 2Fe + 6HCl 2FeCl 3 + 3H 2

Types of chemical reactions 4.Double displacement: When 2 molecules switch elements. AgNO 3 + HCl AgCl + HNO 3

Review 1.Fe + S FeS 2.2 Mg + O 2 2 MgO 3.Na 2 O + H 2 O 2 NaOH 4.CuCO 3 CuO + CO 2 5.Fe + H 2 SO 4 FeSO 4 + H 2 6.AgNO 3 + NaCl AgCl + HNO 3

Answers to review 1.Synthesis 2.Synthesis 3.Synthesis 4.Decomposition 5.Single Displacement 6.Double displacement

Rules of chemical reactions Law of conservation of matter: –The number of atoms of each element produced is the same as the number of atoms in the reactants. ie.H 2 + O 2 H 2 O 2H 2 + O 2 2H 2 O Creating a balanced equation helps demonstrate this law.

Balancing Chemical Equations All chemical equations must demonstrate the Law of conservation of matter. Begin by balancing the metals Then Poly atomic ions Then non-metals Then hydrogen Lastly, balance oxygen.

Balancing Chemical Equations Example: Al + O 2 Al 2 O 3 1.Al on the left = 1; Al on the right = 2. Put a 2 in front of the Al on the left. 2Al + O 2 Al 2 O 3 2. O on the left = 2; O on the right = 3. Put a 3 in front of O on the left and 2 in front of Al on the right. 2Al + 3O 2 2Al 2 O 3 NOTICE: The Al’s do not match. To balance the Al’s use a multiple of all three numbers (2Al=2; 2Al 2 =4) Since Al = Al 1 and 1*4 = 4. then the balanced formula is… 4Al + 3O 2 2Al 2 O 3 **Now we have 4Al’s and 6O’s on each side.

Review 1.S + H 2 SO 4 SO 2 + H 2 2.NaCl + BeF2 NaF + BeCl2 3.Ca(OH) 2(aq) + HCl (aq) CaCl 2(aq) + H 2 O (l) 4.CH 4 + O 2 CO 2 + H 2 O 5.Mg + Mn 2 O 3 MgO + Mn