Agenda:  Warm-up: Word Equations  Chemical reactions and energy  Endothermic or exothermic  How energy is represented in chemical reactions  Practice: Predicting products  Using types of reactions  Cards Homework:

 #13 Zinc II hydroxide + hydrochloric acid Zinc II chloride + water #17 Sodium carbonate + sulfuric acid Sodium sulfate + water + carbon dioxide

Representing the energy changes in reactions Thermo-chemistry

1.When two chemicals mix their temperature rises: 2.A solid burns brightly and releases heat, light and sound: 3.When two chemicals are mixed their temperature drops: 4.Two chemicals will only react if you heat them continually: 5.Plants take in light energy for photosynthesis:

During chemical reactions, the bonds between atoms break and new bonds are formed. Energy must be absorbed to break bonds. When bonds are made, energy is released Copper II carbonate reacts to form copper II oxide and carbon dioxide Is this reaction endothermic or exothermic? Examine the bonds to determine the answer.

Notes: Representing energy in chemical reactions 1. Measurement of energy: joules Joules/gram or joules/mole 2. Energy shown as a reactant or product Endothermic: Exothermic: 3. Change in energy: ∆H (heat of reaction) Positive + ∆ Negative -∆ 4. Diagrams of the energy

ENERGY IN REACTIONS Exothermic reactions Energy is given out The products have less energy than the reactants Exothermic reactions are common. Combustion and neutralization (a special type of double replacement reactions) are exothermic

ENERGY LEVEL DIAGRAMS Exothermic reactions energy

ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction

ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction reactants

ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction reactants products

ENERGY LEVEL DIAGRAMS Exothermic reactions energy course of reaction reactants products energy given out ∆H is negative

ENERGY LEVEL DIAGRAMS Endothermic reactions Energy is taken in The products have more energy than the reactants The energy is taken in from the surroundings

ENERGY LEVEL DIAGRAMS Endothermic reactions energy

ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction

ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction reactants

ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction reactants products

ENERGY LEVEL DIAGRAMS Endothermic reactions energy course of reaction energy taken in ∆H is positive reactants products

SUMMARY TABLE Exothermic reactions Endothermic reactions

SUMMARY TABLE Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings

SUMMARY TABLE Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings ∆H is negative∆H is positive

SUMMARY TABLE Exothermic reactions Endothermic reactions Energy is given out to the surroundings Energy is taken in from the surroundings ∆H is negative∆H is positive Products have less energy than reactants Products have more energy than reactants

∆H = ENTHALPY = CHANGE IN ENERGY How much energy is given out or taken in? Energy is needed to break chemical bonds Energy is given out when bonds are made ∆H is the difference between the energy needed to break the bonds in the reactants, and the energy given out when new bonds are made in the products

WORKING OUT ∆H Summary The energy values have units of kJ/mole ∆H is difference between energy in – energy out Energy goes in to break bonds Energy goes out when bonds are made

 Most exothermic reactions require energy to start the reaction. A catalyst speeds up a reaction by lowering the amount of activation energy needed. Energy Course of the reaction

the overall exothermic or endothermic energy change is the same for both the catalysed or uncatalysed reaction. The catalyst might help break the bonds BUT it cannot change the actual bond energies.

Practice: Reactions  Determine types of reactions  Determine if the reaction is endothermic or exothermic