Changes of Matter Physical Change- a change that alters the appearance or form of a substance but doesn’t make the substance into another substance. Ex: flatten or pull on a marshmallow Chemical Change/Reaction- a change in matter that produces one or more new substances. Ex: toasting a marshmallow Physical Change- a change that alters the appearance or form of a substance but doesn’t make the substance into another substance. Ex: flatten or pull on a marshmallow Chemical Change/Reaction- a change in matter that produces one or more new substances. Ex: toasting a marshmallow

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: the reactions that occur when frying an egg. Exothermic Reactions- a reaction in which energy is released. Ex: the burning of airplane fuel Can you name other endothermic or exothermic reactions? Endothermic Reactions- a reaction in which energy is absorbed. Not all endothermic reactions result in a decrease in temperature. Ex: the reactions that occur when frying an egg. Exothermic Reactions- a reaction in which energy is released. Ex: the burning of airplane fuel Can you name other endothermic or exothermic reactions?

What Are Chemical Equations? A short easy way to show a chemical reaction using symbols instead of words. Ex: CO 2 & H 2 O Structure of an Equation *Reactants-substances you start with *Products-substances you end up with *Arrow means yields CaCO 3 yields CaO + CO 2 A short easy way to show a chemical reaction using symbols instead of words. Ex: CO 2 & H 2 O Structure of an Equation *Reactants-substances you start with *Products-substances you end up with *Arrow means yields CaCO 3 yields CaO + CO 2

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.

Open and Closed Systems Open system-matter can enter from or escape to the surroundings. Example: striking a match Closed system-matter is not allowed to enter or leave. Example: a pear decaying under a glass. Open system-matter can enter from or escape to the surroundings. Example: striking a match Closed system-matter is not allowed to enter or leave. Example: a pear decaying under a glass.

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 2 yields 2H 2 O 2 Can you balance the following? Mg + O 2 yields MgO 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 2 yields 2H 2 O 2 Can you balance the following? Mg + O 2 yields MgO

Classifying Chemical Reactions Synthesis-two or more elements or compounds combine to make a more complex substance. Decomposition-breaks down compounds into simpler products. Replacement-one element replaces another in a compound, or when two elements or compounds trade places. Synthesis-two or more elements or compounds combine to make a more complex substance. Decomposition-breaks down compounds into simpler products. Replacement-one element replaces another in a compound, or when two elements or compounds trade places.

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(enzymes in cells) and Inhibitors Chemists can control rates of reactions by changing factors such as: Surface Area Temperature Concentration Use of Catalysts(enzymes in cells) and Inhibitors