Reviewing Bonding My turn: Polyatomic ions are ionic compounds made from more than one atom. Ionic compounds are electrically neutral. The subscript numbers indicate the number of ions in the compound. The positive ion is written first in an ionic compound.

Reviewing Bonding Your turn: Properties of compounds? Properties of metals? Polar versus nonpolar?

Observing Chemical Change State how changes in matter can be described. Explain how you can tell when a chemical reaction occurs. √ √ √ √ √ √ √ √

Vocabulary Review Reactants and products Matter-anything that has mass and takes up space Chemistry-the study of matter and how matter changes Physical properties and Chemical properties Physical and Chemical change (salt in water versus burning wood) Reactants and products

Bonding and Chemical Change Chemical changes when bonds break and new bonds form.

Evidence for Chemical Reactions Change in properties and change in energy (only sure evidence) Change in physical properties…new substances color Precipitate (solid formed during a chemical reaction) A gas from solid or liquid reactants Physical properties such as texture and harness may also change Moist dough becomes a dry, porous solid after baking

More on Chemical Reactions Changes in chemical properties Na and Cl are reactive elements but their product (NaCl) is stable One or more new substances are produced in a chemical reaction When an electric current is passed through water (electrolysis) H2 (gas) and O2 (gas) are produced.

Review Endothermic Reaction Chemical reactions occur when bonds break and new bonds form. They usually absorb heat or liberate heat(release it). Endothermic reactions absorb energy when the bonds break Energy is absorbed from nearby matter Often temperature changes Baking soda combined with vinegar absorbs heat, making it feel colder When heat is added constantly, (egg frying)

Review: Exothermic Reaction The making or breaking of chemical bonds results in a net release of energy Energy typically releases as heat Fuel and oxygen in the plane’s engine release heat causing the gases in the engine to expand. This moves the gases out of the plane which exerts a force that moves the plane forward.

Bonding and Chemical Change

Describing Chemical Reactions Identify what information a chemical equation contains. Explain how matter is conserved during a chemical reaction. Explain what a balanced chemical equation must show. Name three types of chemical reactions. √ √

Chemical Formulas The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

What Are Chemical Equations? Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

Reviewing the Law of Conservation of Matter Matter is neither created nor destroyed *It is simply rearranged!

Conservation of Matter The law of conservation of matter states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

Open and Closed Systems

Balancing Chemical 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.

Let’s try some! 3 3 ____ AlBr3 + ____ K  ____ KBr + ____ Al Count the atoms: 1 Aluminum atom 1 Potassium atom 1 Potassium atom 1 Aluminum atom 3 Bromine atoms 1 Bromine atom Is it balanced? No! Add coefficients to balance atoms: 1 Aluminum atom 3 Potassium atoms 3 Potassium atoms 1 Aluminum atom 3 Bromine atoms 3 Bromine atoms Is it balanced? YES!

Let’s try some! ____ FeO + ____ PdF2  ____ FeF2 + ____ PdO Count the atoms: 1 Iron 1 Palladium 1 Iron 1 Palladium 1 Oxygen 2 Flourine 2 Flourine 1 Oxygen Is it balanced? YES! Do we need to add coefficients? NO!

Let’s try some! 6 4 ____ P4 + ____ Br2  ____ PBr3 Count the atoms: 4 Phosphorus 2 Bromines 1 Phosphorus 3 Bromines Is it balanced? No! Add coefficients to balance atoms: 4 Phosphorus 12 Bromines 4 Phosphorus 12 Bromines Is it balanced? YES!

Let’s try a harder one! 2 3 3 ____ CoBr3 + ____ CaSO4  ____ CaBr2 + ____ Co2(SO4)3 Count the atoms: 1 Co 1 Ca 1 Ca 2 Co 3 Br 1 S 2 Br 3 S 4 O 12 O Is it balanced? No! Add coefficients to balance atoms: 2 Co 3 Ca 3 Ca 2 Co 6 Br 3 S 6 Br 3 S 12 O 12 O Is it balanced? YES!

Classifying Chemical Reactions Three general types of chemical reactions 1. Synthesis: Two or more elements or compounds combining to make a more complex substance 2. Decomposition Compounds break down into simpler products (hydrogen peroxide decomposes to water and oxygen gas) 3. Replacement One element replaces another in a compound or two elements in different compound trade places (Copper can be obtained by heating copper oxide with carbon. The carbon takes the place of copper.

Controlling Chemical Reactions Explain how activation energy is related to chemical reactions. Identify factors that affect the rate of a chemical reaction.

Energy and Reactions Activation Energy is the minimum amount of energy needed to start a chemical reaction Chemical reactions require activation energy to get started. The energy is used to break the chemical bonds of the reactants so the atoms can begin to form the new chemical bonds of the products. Example: Hydrogen and oxygen form water Reaction gives off a large amount of energy(exothermic) Electric spark (energy) gives enough activation energy for the molecules to react

Exothermic and Endothermic Reactions Every chemical reaction needs activation energy. Whether or not is needs more energy depends on if it is exothermic or endothermic. Exothermic: products have less energy than the reactants at the end (burning of fuel) Endothermic: needs energy to keep going besides activation energy; energy of the products is higher than that of the reactants How are the two graphs the same? (Both graphs plot energy against time for chemical reactions. In both graphs, the reaction begins when energy rises to a peak, the activation energy, which is about the same for both reactions.) How are the two graphs different? (The graph on the left is for an exothermic reactions, and the graph on the right is for an endothermic reaction. In the exothermic reaction, heat is released, and the products have les energy than the reactants. In the endothermic reactions, heat is absorbed, and the products have more energy than the reactants.) If the energy level for the exothermic reaction had started out as low as the energy level for the endothermic reaction, would the activation energy also be lower? Why? (No, because the activation energy is the minimum amount of energy required to sate the reaction.)

Factors Affecting Rates of Chemical Reactions 1. Surface Area When a chunk of solid substance reacts with a liquid or gas, only the particles on the surface of the solid come into contact with the other reactant. But if you break the solid into smaller pieces, more particles are exposed and the reactions happens faster. (Chewing your food breaks it into smaller pieces that your body can digest more easily and quickly.) 2. Temperature The higher the temperature the faster the reactions (faster-moving particles have more energy) Example: Bacteria in milk 3. Concentration The higher the concentration of the reactants the more particles react

Factors Affecting Rates of Chemical Reactions Continued 4.Catalysts A catalyst is a material that increases the rate of reaction by lowering the activation energy. They are not reactants because they aren’t permanently changed by the reaction. Enzymes in your body are specific examples of a catalysts. Each one is specific, affecting only one chemical reaction. 5. Inhibitors Inhibitors slow down the rate of chemical reactions. They prevent the reactants from coming together. Preservatives added to food products prevent them from becoming stale or spoiling. 5.

Fire and Fire Safety List the three things necessary to maintain a fire. Explain why you should know about the causes of fire and how to prevent a fire.

Understanding Fire The Fire Triangle Combustion reaction= reaction between oxygen and fuel (exothermic) Fuel = material that releases energy when it burns (oil, wood, natural gas, paper) Burning wood is an example of a chemical change. The Fire Triangle Fuel, oxygen (20% of air)and heat (a lighted match, electric spark or heat from a stove)

Home Fire Safety- Be Prepared Fighting Fires CO2 can smother fie (baking soda decomposes into CO2) Smother a saucepan on fire with a lid Controlling Fire Focus on removing one part of the fire triangle Water removes two parts of the triangle Fire extinguisher (The best way!) Call the fire department Preventing Trouble- the best form of fire safety! Fire safe house