Ch 7 Chemical Reactions

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. 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

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

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

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