Chemical Reactions

Changes In Matter Changes in matter can be described in terms of physical and chemical changes. Physical changes- alters the form or appearance of a substance but does not make the substance into another substance. Chemical changes- a change in matter that produces one or more new substances. Chemical changes occur when bonds break and new bonds form.

Evidence of Chemical Change Color change (leaves on trees) Precipitate formation- A solid that forms when two solutions are mixed. Gas production (Oxygen from photosynthesis) Change in properties (baking bread)

What Are Chemical Equations? Chemical equations are a short, easy way to show a chemical reaction. Scientist use chemical formulas and other symbols instead of words to summarize a reaction.

The Structure of an Equation The materials at the beginning of the reaction are called the reactants, when the reaction is complete you have the products. reactant + reactant product + product “yields” The number of reactants and products can vary. Ex: reaction that occurs when limestone is heated:

How do you describe this reaction in words: CaCO3 CaO + CO2 In this reaction, the reactant calcium carbonate yields the products calcium oxide and carbon dioxide.

The Law Conservation of Mass The total mass of the reactant must equal the total mass of the products. Matter cannot be created or destroyed. The number and type of atoms present at the start of the reaction must be present at the end.

Classifying Chemical Reactions Synthesis Decomposition Replacement (Single or Double)

Synthesis Reaction 2 or more elements or compounds combine to form a more complex substance. Ex. A + B AB H2 + O H2O

Decomposition Reaction Breaks down compounds into simpler products Ex. AB A + B 2H2O2 2H2O + O2

Replacement Reaction Single- When one element replaces another in a compound Ex: ab + c a + cb 2Cu2O + C 4Cu + CO2 Double- When two elements in different compounds trade places. ab + cd ad + cb FeS + 2HCl FeCl2 + H2S