1. Describing Chemical Reactions

2. Chemical Equations
A chemical equation uses symbols and chemical formulas to show a reaction.
Chemical equations show the substances you begin with (called reactants) and the new substances produced (products)
Reactant + reactant → product + product
Some reactions may have more reactants and products, and some may have less.
CaCO3 → CaO + CO2

3. Classifying Chemical Reactions
3 categories:
Synthesis: 2 or more elements/compounds combine to make a new and more complex product.
Ex: 2H2 + O2 → 2 H2O
Decomposition: compounds are broken down into simpler products.
Ex: H2O2 → 2 H2O + O2
Replacement: one element replaces another element in a compound (In a double replacement, 2 elements trade places).
single: 2Cu2O + C → 4Cu + CO2 (single).
double:FeS + 2HCl → FeCl2 + H2S (double).

4. Why Balance Equations?
Remember that the law of conservation of mass states that matter is neither created nor destroyed in any chemical reaction.
So in any chemical equation, the total mass of the reactants must equal the total mass of the products.
There are two kinds of systems in which reactions occur:
1. open system- matter can either enter or escape. Ex: burning a match.
2. closed system- matter cannot enter or leave. Ex: fruit decaying in a sealed jar.

5. Balancing Chemical Equations
For a reaction to be accurate, the chemical equation must show the same number of each type of atom on both sides of the equation for the equation to be balanced.
To balance an equation:
1. Write the equation:
Ca + O2 → CaO
2. Count the atoms on both sides.
Reactants: 1 calcium, 2 oxygen.
Products: 1 calcium, 1 oxygen.
3. Use coefficients (the number in front of the symbol that tells you how many atoms or molecules there are) to balance atoms.
__Ca + O2 → __CaO
4. Check the equation.
Reactants: 2 calcium, 2 oxygen.
Products: 2 calcium, 2 oxygen

6. Section 1
1. What is the difference between a physical property and a chemical property?
2. There are two ways to know if a chemical reaction took place. What are they and give one example of each.
3. What is a precipitate?
4. In terms of chemical bonds, what happens during a chemical reaction?
5. Why would a change in temperature indicate that a chemical reaction occurred?

7. 6. What do we use to represent a chemical reaction?
7. What is the difference between a reactant and a product
8. Identify the reactants and the products in the reaction Mg + O2  MgO.
9. Define the principle of Conservation of Mass (not the law of conservation of mass) and explain its importance when balancing equations.
10. How is an open system different from a closed system?

8. Practice! 1. __Fe + __O2 → __ Fe2O3 2. __ H2 + __ O2 → __ H2O
3. __ N2 + __ H2 → __ NH3
4. __ S8 + __ O2 → __ SO3
5. __ HgO → __ Hg + __ O2
6. __ N2 + __ O2 → __ N2O
7. __ SiCl4 + __ H2O → __ H4SiO4 + __ HCl
8. __ SO2 + __O2 → __ SO3

9. ___CH4 + ___O2  ___CO2 + ___H2O ___S8 + ___O2  ___SO2 ___K + ___Br2  ___Kbr ___Al +___ O2  ___Al2O3 ___Na2O2 + ___H2O  ___NaOH + ___O2

10. More Practice! 1. __SnO2 + __H2 → __ Sn + __H2O
2. __ H2 + __ O2 → __ H2O
3. __ N2 + __ H2 → __ NH3
4. ___ AgI + ___ Fe2(CO3)3  ___ FeI3 + ___ Ag2CO3
5. ___ C2H4O2 + ___ O2  ___ CO2 + ___ H2O
6. ___ C2H6 + ___ O2  ___ CO2 + ___ H2O
7. ___ V2O5 + ___ CaS  ___ CaO + ___ V2S5

11. Even More Practice! 5. __ C3H8 + __ O2 → __ CO2 + __ H2O
1. __BaCl2 + __H2SO4 → __ BaSO4 + __HCl
2. __ Pb(NO3)2+ __ AlCl3 → __ PbCl2+ __ Al(NO3)3
3. __ AlBr3 + __ Cl2 → __ AlCl3 + __ Br2
4. __ C2H2 + __ O2 → __ CO2 + __ H2O
5. __ C3H8 + __ O2 → __ CO2 + __ H2O

12. 1. __Al2(SO3)3  +  __NaOH  →  __ Na2SO3 +  __ Al(OH)3   
2. __ Al2O3  + __ Fe   → __ Fe3O4  +  __ Al   
3. __ KClO3    → __ KCl   + __ O2   
4. __ NH4NO3  → __ N2O  + __ H2O   
5. __ NaHCO3    → __ Na2CO3   + __ H2O  + __ CO2   
6. __ Be2C   + __ H2O    → __ Be(OH)2     + __ CH4   
7. __ S    + __ HNO3  → __ H2SO4   + __ NO2   + __ H2O   
8. __ Cu   + __ HNO3 → __Cu(NO3)2  + __ NO +  __ H2O

13. ___CH4 + ___O2  ___CO2 + ___H2O ___S8 + ___O2  ___SO2
11. What four steps are needed to balance an equation?
12. Balance the following equations:
___CH4 + ___O2  ___CO2 + ___H2O
___S8 + ___O2  ___SO2
___K + ___Br2  ___KBr
___Al +___ O2  ___Al2O3
___Na2O2 + ___H2O  ___NaOH + __O2

14. ____ N2 + ____ H2 → ____ NH3
2) ____ KClO3 → ____ KCl + ____ O2
3) ____ NaCl + ____ F2 → ____ NaF + ____ Cl2
4) ____ H2 + ____ O2 → ____ H2 O
5) ____ Pb(OH)2 + ____ HCl → ____ H2O + ____ PbCl2
6) ____ AlBr3 + ____ K2SO4 → ____ KBr + ____ Al2(SO4)3
7) ____ CH4 + ____ O2 → ____ CO2 + ____ H2O
8) ____ C3H8 + ____ O2 → ____ CO2 + ____ H2O

15. Quiztime! Physical or Chemical?