1. Chemical Reactions
Chapter 11

2. Writing chemical equations
To write a word equation: write names of reactants left of the arrow separated by plus signs; write names of products right of the arrow separated by plus signs.
Hydrogen + oxygen  water

3. Skeleton equation
Chemical equation that does not indicate amounts of the reactants and products.
Not balanced!
H2(g) + O2(g)  H2O(l)
Catalyst is a substance that speeds up the reaction but is not consumed in the reaction. Neither reactant or product and written above the arrow.

4. Balancing equations
Coefficients: small whole numbers that are placed in front of the formulas in an equation in order to balance it.
A balanced equation is where each side of the equation has equal numbers of atoms of each element and mass is conserved.

5. Balancing equations First write the skeleton equation
Then use coefficients to balance the equation so that it obeys the law of conservation of mass.
Never change subscripts.
Simplify if possible

6. Chemical reactions The five general types of reactions are:
Combination
Decomposition
Single-replacement
Double-replacement
Combustion
*Chemical change occurs
with all of them!

7. Combination Reactions
Two or more substances react to form a single new substance.
2Mg(s) + O2(g)  2MgO(s)

8. Decomposition A single reactant forms 2 or more products
2HgO(s)  2Hg(l) + O2(g)

9. Single-Replacement Reactions
One element replaces a second element in a compound.
Both the reactants and products have a single element and a compound.
Activity series: lists metals in order of decreasing reactivity. Page 333
A reactive metal will replace any metal listed below it in the activity series. A reactive halogen will replace any halogen below it.

10. Single-replacement reactions
Br2(aq) + NaI(aq)  NaBr(aq) + I2(aq)
Br2(aq) + NaCl(aq)  No reaction

11. Double-Replacement Reactions
Exchange of positive ions between two compounds.
Aqueous solutions
Form a precipitate (solid), a gas, or a molecular compound such as water
Na2S(aq) + Cd(NO3)2(aq)  CdS(s) + 2NaNO3(aq)
2NaCN(aq) + H2SO4(aq)  2HCN(g) + Na2SO4(aq)
Ca(OH)2(aq) + 2HCl(aq)  CaCl2(aq) + 2H2O(l)

12. Combustion Reaction
An element or a compound reacts with oxygen often producing energy in the form of heat and light.
Always involves oxygen as a reactant.
The other reactant is usually a hydrocarbon (compound composed of carbons and hydrogens).
Products are carbon dioxide and water for complete combustion.

13. Combustion Reaction 2C8H18(l) + 25O2(g)  16CO2(g) + 18H20(l)
Reactions between oxygen and some elements other than carbon can also be combustion reactions.
2Mg(s) + O2(g)  2MgO(s)

14. Predicting the products of a chemical reaction
The number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products.
Figure on page