1. Chapter 7
Chemical Reactions

2. Vocab
Reactants
Products
Chemical Equations
Coefficients

3. Chemical Equations Law of Conservation of Mass -
Mass cannot be created or destroyed.
The mass of the reactants must equal the mass of the products in a chemical reaction.

4. Balancing Chemical Equations
In other words,
The total number of each type of atom must be the same on both sides of the equation.

5. Do’s and Don’ts
Do:
Write the equation with the correct symbols and formulas
Count the number of atoms on each side.
Use coefficients to change the totals.
Check your work by recounting.

6. Do’s and Don’ts Don’t: Change subscripts!
Change the chemical formulas or symbols.
Add coefficients in the middle of a formula.

7. Balancing Equations
H2 +O H20
What happened to the other O?
It can’t just disappear. Mass must be conserved.

8. Balancing Equations
C + H CH4 2

9. Some to try.
Zn + HCl ---> ZnCl2 + H2
KClO3 ---> KCl + O2
S8 + F2 ---> SF6
Fe + O2 ---> Fe2O3
C2H6 + O2 ---> CO2 + H2

10. Types of Chemical Reactions
Synthesis
Decomposition
Single Replacement
Double Replacement
Oxidation/Reduction
Combustion

11. Synthesis
Combining two or more simple substances to make a more complex one.
A + B AB
2Na +Cl NaCl

12. Decomposition
A complex substance breaks down into two or more simpler substances
AB A + B
2 H2O H2 + O2

13. Single Replacement
An uncombined element replaces an element that is part of a compound.
A + BX AX + B
Zn + 2HCl ZnCl2 + H2

14. Double Replacement Atoms in different compounds trade places
AX + BY AY + BX
CaCO3 + H2SO CaSO4 + H2CO3

15. Combustion

16. Energy of Reactions Exothermic – gives off energy
Endothermic – absorbs energy.
Activation Energy – energy required to start a reaction.

17. Reaction Rates Increasing Temperature increases reaction rate
Surface Area – increasing the surface area increases the rate of reaction.
Concentration – amount of reactants in a given volume.
Stirring increases reaction rate
Catalyst – speeds up a reaction but does not change during the reaction