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:
WORD EQUATIONS: HAND-INWRITE THE FORMULAS AND BALANCE
#13 Zinc II hydroxide + hydrochloric acid
Zinc II chloride + water
#17 Sodium carbonate + sulfuric acid Sodium sulfate + water + carbon dioxide
ENERGY IN REACTIONS
Representing the energy changes in reactionsThermo-chemistry
Representing energy in chemical reactions1. Measurement of energy: joules
Joules/gram or joules/mole2. 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 positivereactants
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
ENERGY
