Chemical Reactions

Chapter 21: Sec 1&2

Chemical Reactions

• a change of one or more substances converted into new substances

• Ex. Iron mixed w/the oxygen in theair to form rust

Chemical Reactions

1. Reactants – substances that combine or change

2. Products – new substances that are produced

Reactants Products

• Butt of the arrow are the reactants and point of the arrow is the products

Reactants ProductsProduce

Conservation of Mass

• A law which states that, in a chemical reaction matter is not created or destroyed; it stays the same

• French chemist Antoine Lavoisier– experimented with mercury (II) oxide and heat– found mass of products (liquid mercury and oxygen gas)

equaled the mass of reactants

• Mass of reactants = mass of products

Writing equations

• chemical equation – uses chemical formulas and symbols to describe a chemical reaction and the product(s) it produces

Chemical Equations

1. Chemical formula express the relationship between the elements in the compounds and molecule they make up

2. Coefficients – numbers which represent the number of units of each substance in a reaction

3. Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products

4. Subscripts – numbers which represent the number of atoms in a molecule of a particular element

Symbols used in chemical equations

Symbol Meaning

produces or forms+ Plus

(s) solid(l) liquid(g) gas

(aq) aqueous, a substance is dissolved in water

heat the reactants are heated

light the reactants are exposed to liqht

elec. an electric current is applied to the reactants

Balanced Equations

• both sides of the equation have same number of atoms of each element– (remember law of conservation of mass)

• Coefficients used to balance the amount of reactants and products

Writing balanced equations

1. describe the reaction in words2. write the equation using formulas and

symbols3. check for balance4. add coefficients where needed for balance