Changes of Matter Physical Change- a change that alters the appearance or form of a substance but doesn’t produce a new substance. Ex: melting a sample of gold Chemical Change/Reaction- a change in matter that produces one or more new substances. Ex: Gas produced from vinegar and baking soda.

Evidence for Chemical Reactions Gas Production Change in Temperature/Energy Change in Color Change in Properties Formation of a Precipitate

Changes in Energy Endothermic Reactions- a reaction in which energy is absorbed. Not all endothermic reactions result in a decrease in temperature. Ex: frying an egg Exothermic Reactions- a reaction in which energy is released. Ex: the burning of airplane fuel

Chemical Formulas A chemical formula is a combination of symbols that represents the elements present in the formula and the ratio of elements present. Ex: MgCl2 - One atom of magnesium for every two atoms of chlorine. Ratio is 1:2 How many total atoms are present in the following: Pb(NO3)4 H2SO4 2HNO3

What Are Chemical Equations? Using formulas and symbols instead of words to represent a chemical reaction. Ex: CaCO3 ------- CaO + CO2 Structure of an Equation *Reactants-substances you start with *Products-substances you end up with *Arrow means “yields”

Subscripts vs. Coefficients Subscripts – A number that indicates the ratio of elements in a compound. Ex: H2O Ratio 2:1 Coefficients – a number in front of a chemical formula in an equation that indicates how many molecules or atoms of each reactant and product are involved in a reaction. Ex: 3H2O Three molecules of water

Conservation of Mass During a chemical reaction, matter is not created or destroyed. Total mass of the reactants equals the total mass of the products. Open System – matter can enter from or escape to the surroundings. Ex: burning wood in a fireplace Closed System – matter is not allowed to enter or leave. Ex: a chemical reaction in a sealed bag

Balancing Equations To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation. Ex: 2H2O + O2  2H2O2 (4 hydrogen atoms and 4 oxygen atoms are present on both sides of the equation)

Try these!! _Na + Cl2  _NaCl Ca + Cl2  CaCl2 _H2O  _H2 + O2 N2 + _H2  _NH3 _Al2O3  _Al + _O2 P4 + _O2  P4O6 _Fe + _H2O  Fe3O4 + _H2

Controlling Chemical Reactions All reactions require a certain amount of activation energy to get them started. Activation energy – the minimum amount of of energy needed to start a chemical reaction.

Factors that Influence the Rate of Reactions Surface Area Temperature Concentration – amount of substance in a given volume Use a Catalyst – a material that increases the rate of a reaction Use an Inhibitor – a material that decreases the rate of a reaction