Agenda: April 12th  Warm-up: A change requires energy.  Chemical reactions and energy  Endothermic or exothermic  How energy is represented in chemical reactions  Practice: Predicting products  Mixed Practice

Representing the energy changes in reactions Thermo-chemistry

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

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