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) + H2O(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. 2H2 + O2 2H2O

2. Decomposition: when a compound breaks up into its individual parts.

ie. 2H2O 2H2 + O2

Types of chemical reactions

3. Single displacement: when one element is removed from a molecule and replaced by another element.

ie. 2Fe + 6HCl 2FeCl3 + 3H2

Types of chemical reactions

4. Double displacement: When 2 molecules switch elements.

AgNO3 + HCl AgCl + HNO3

Review

1. Fe + S FeS

2. 2 Mg + O2 2 MgO

3. Na2O + H2O 2 NaOH

4. CuCO3 CuO + CO2

5. Fe + H2SO4 FeSO4 + H2

6. AgNO3 + NaCl AgCl + HNO3

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. H2 + O2 H2O

2H2 + O2 2H2O

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 + O2 Al2O3

1. Al on the left = 1; Al on the right = 2. Put a 2 in front of the Al on the left.2Al + O2 Al2O3

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 + 3O2 2Al2O3

NOTICE: The Al’s do not match. To balance the Al’s use a multiple of all three numbers (2Al=2; 2Al2=4) Since Al = Al1 and 1*4 = 4. then the balanced formula is…4Al + 3O2 2Al2O3

**Now we have 4Al’s and 6O’s on each side.

Review

1. S + H2SO4 SO2 + H2

2. NaCl + BeF2 NaF + BeCl2

3. Ca(OH)2(aq) + HCl(aq) CaCl2(aq) + H2O(l)

4. CH4 + O2 CO2 + H2O

5. Mg + Mn2O3 MgO + Mn