Chapter 6 Chemical Reactions and Equations 6.1 Chemical Equations 6.2 Types of Reactions 6.3 Nature of Reactions

6.1 Chemical Equations Objectives Relate chemical changes and macroscopic properties. Demonstrate how chemical equations describe chemical reactions. Illustrate how to balance chemical reactions by changing coefficients.

Recognizing Chemical Reactions Chemical reactions occur all around you and within you. Evidence: Color change Odor Temperature change Gas production Precipitate

Writing Chemical Equations Reactant- substance that undergoes a reaction, the starting substance(s). Product- the new substance formed from the reactants. Rust Iron and oxygen react to form Iron (III) oxide

Writing Chemical Equations Word Equations Chemical Equations First lets practice writing formulas. You MUST be able to write formulas in order to write the equations

Word Equation Word equation Word equations are the simplest form Vinegar + Baking soda  sodium acetate + water + carbon dioxide Can be using common names or the chemical names. Acetic acid + sodium hydrogen carbonate  sodium acetate + water + carbon dioxide Word equations are the simplest form

Chemical Equations Uses the chemical formulas for the reactants and products. This is why you must be able to write formulas. Baking soda and vinegar HC2H3O2 + NaHCO3  NaC2H3O2 + H2O + CO2

Chemical Equations It is also important to know the state the compounds are in (g) – gas (s) – solid (l) – liquid (aq) – aqueous HC2H3O2 (aq) + NaHCO3 (s)  NaC2H3O2 (aq) + H2O (l) + CO2 (g)

Equations and Energy Some chemical reactions require an energy input to occur Some chemical reaction produce energy Energy can be in the form of electricity (input), heat or light. Endothermic reaction- absorbs energy Exothermic reaction- gives off energy

Balancing Chemical Equations Balanced equation for the reaction of iron and chlorine: 2Fe (s) + 3 Cl2 (g)  2FeCl3 (s) To balance an equation you must first find the correct coefficients- the number written in front of a reactant or product; tells the smallest number of particles of the substance involved in the reaction.

Steps for balancing equations Write the skeleton equation for the reaction. Count the atoms of the elements in the reactants. Count the atoms of the elements in the products. Change the coefficients to make the number of atoms of each element equal on both sides of the equation. Write the coefficient in their lowest possible ratio. Check your work.