chapter 4

law of conservation of mass

• mass is neither created or destroyed during a chemical reaction

chemical reactions are represented by writing chemical equations. there are two types:

1. word equation

2. formula and symbol equations (called chemical equation)

word equation

• simplest type of equation

• in a word equation we have

  • the names of the starting substances - reactants - are written on the left hand side

  • the names of the new substances - products - are written on the right hand side

  • an arrow -> shows the direction of the reaction

  • a plus (+) sign shows 2 or more reactants are added together (and/or 2 or more products are formed)

reactant & product

• a substance that undergoes a change in a chemical reaction

• a substance produced in a chemical reaction

chemical equation

• a representation of a chemical reaction using symbols of the elements and compounds to indicate the amount of substance of each reactant and product

• chemical equations must be balanced

• the state of the substance

• the number of atoms of each element in the reactants must be equal to the number of products to obey the law of conservation of mass

chemical equation steps

1. write the formulas

   • K^(S) + Cl^2(g) -> KCl^(S)

2. balance out the species using large numbers to ensure atoms of reactants = atoms of products

   • 2K^(S) + Cl^2(g) -> 2KCl^(S)