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 ice Chemical Change/Reaction- a change in matter that produces one or more new substances. Ex: Gas produced from vinegar and baking soda. Physical Change- a change that alters the appearance or form of a substance but doesn’t produce a new substance. Ex: melting ice 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 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 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 shows the ratio of elements in a compound. Ex: MgCl 2 - One atom of magnesium for every two atoms of chlorine. Ratio is 1:2 How many total atoms present in the following: Pb(NO 3 ) 4 H 2 SO 4 2HNO 3 A chemical formula is a combination of symbols that shows the ratio of elements in a compound. Ex: MgCl 2 - One atom of magnesium for every two atoms of chlorine. Ratio is 1:2 How many total atoms present in the following: Pb(NO 3 ) 4 H 2 SO 4 2HNO 3

What Are Chemical Equations? Using formulas and symbols instead of words to represent a chemical reaction. Ex: CaCO  CaO + CO 2 Structure of an Equation *Reactants-substances you start with *Products-substances you end up with *Arrow means “yields” Using formulas and symbols instead of words to represent a chemical reaction. Ex: CaCO  CaO + CO 2 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: H 2 O 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: 3H 2 O Three molecules of water Subscripts – A number that indicates the ratio of elements in a compound Ex: H 2 O 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: 3H 2 O Three molecules of water

Conservation of Mass During a chemical reaction, matter is not created or destroyed. All atoms present at the start of a reaction are present at the end. Total mass of the reactants equals the total mass of the products. During a chemical reaction, matter is not created or destroyed. All atoms present at the start of a reaction are present at the end. Total mass of the reactants equals the total mass of the products.

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: 2H 2 O + O  2H 2 O 2 (4 hydrogen atoms and 4 oxygen atoms are present on both sides of the equation) 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: 2H 2 O + O  2H 2 O 2 (4 hydrogen atoms and 4 oxygen atoms are present on both sides of the equation)

Try these!! _Na + Cl 2  _NaCl Ca + Cl 2  CaCl 2 _H 2 O  _H 2 + O 2 N 2 + _H 2  _NH 3 _ Al 2 O 3  _Al + _O 2 P 4 + _O 2  P 4 O 6 _Fe + _H 2 O  Fe 3 O 4 + _H 2 _Na + Cl 2  _NaCl Ca + Cl 2  CaCl 2 _H 2 O  _H 2 + O 2 N 2 + _H 2  _NH 3 _ Al 2 O 3  _Al + _O 2 P 4 + _O 2  P 4 O 6 _Fe + _H 2 O  Fe 3 O 4 + _H 2

Controlling Chemical Reactions All reactions require a certain amount of activation energy to get them started. Chemists can control rates of reactions by changing factors such as: Surface Area Temperature Concentration Use of Catalysts (more activation energy) and Inhibitors (less activation energy) Chemists can control rates of reactions by changing factors such as: Surface Area Temperature Concentration Use of Catalysts (more activation energy) and Inhibitors (less activation energy)