1. Ch 7 Chemical Reactions

2. I. Describing Reactions
A. Chemical Equations:
1. Reactants – substance that undergoes change
2. Products – the new substance formed
a. Reactants → Products
Ex. Carbon + Oxygen → Carbon Dioxide
b. chemical equation – representation in which the reactants and products are expressed as a formula.
Ex. C + O2 → CO2

3. 3. Law of Conservation of Mass – states that mass neither created
or destroyed
Ex. burning charcoal the coal is being converted into carbon dioxide. You could measure the carbon dioxide and it would = the mass of the charcoal and oxygen that reacted.
B. Balancing Equations
1. coefficients – number before the element
a. Only thing you change
2. Never change the subscript – the number following the element
Hydrazine N2H4 + O2 → N2 + H2O
3. mole – one mole = 6.02 x 1023 (Avogadros number) particles of that substance. 2

4. Classifying Reactions
Synthesis (Composition) – two elements combine to form a single substance
A + X  AX
Decomposition – one substance is split into two or more smaller parts
BX  B + X

5. Classifying Reactions… continued
Single replacement – a single element takes the place of an element in a compound
A + BX  B + AX
Double replacement – two compounds trade their positive ions.
AY + BX  BY + AX

6. Classifying Reactions… continued
Combustion – a hydrocarbon is combined with oxygen to create carbon dioxide and water.
Examples:
CH4 + O2  CO2 + H2O
C4H8 + O2  CO2 + H2O