Chemical Reactions

Chemical Equation a short way to show chemical reactions, using symbols instead of words. C + O CO Na + Cl NaCl

Chemical Formula A combination of symbols that represent the elements in a compound – NaCl (table salt) – CO₂ (Carbon dioxide) – NaHCO₃ (baking soda) – Subscripts show the number of atoms of an element in a molecule

Chemical Formula Use figure 9 on page 25 to answer the following questions. How many elements make up rubbing alcohol? How many atoms are in each sugar molecule? Which molecule has 2 elements and 11 atoms? Which compounds have the same number of sodium atoms in their formulas?

Chemical Equations Consist of reactants and products Reactants – the materials at the beginning of the equation Product – the completed material as a result of the reaction of the reactants. Reactant + Reactant Product + Product

Conservation of Mass The amount of matter in a chemical reaction does not change. The total mass of the reactants must equal the total mass of the products.

Balancing Equations H₂ + O₂ H₂0 Balanced? – Are the number of atoms of each element the same on both sides of the equation?

Balance Equations 1. Count the number of atoms of each element on each side of the equation. 2. Add coefficients in front of a chemical formula until the number of each molecule is equivalent on both sides of the equation. H₂ + 0₂ H₂0 H₂ + O₂ 2 H₂O 2 H₂ + O₂ 2 H₂O

Determine the number of atoms of each element. Calculate the number of each kind of atom: – 3 H₂O – 2 H₂SO₄ – 4 Fe₂O₃ – 6 NaCl – NO₂ – When a coefficient is in front of the formula, how do you find the total number of atoms of one kind? – What do you do if there is no coefficient?

Balance Equations Mg + O₂ MgO C + Cl CCl₄ Al₂O₃ Al + O₂

Balancing Equations C + 2 Cl₂ CCl₄ 2 Al₂O₃ 4 Al + 3 O₂

Classifying Chemical Formulas Classified by what happens to the reactants and products. – Synthesis – put together (two or more coming together, making a compound) 2 SO₂ + O₂ + 2 H₂O 2 H₂SO₄ – Decomposition – breaking down of compounds to simpler reactants 2 H₂O₂ 2 H₂O + O₂

Classifying Chemical Formulas – Replacement – one element replaces another in a compound, or when two elements in different compounds trade places 2CuO + C 2Cu + CO₂