HEAT ENERGY IN REACTIONS
Success Criteria
1. I can explain the difference between an
exothermic and endothermic reaction and give
examples of each
STARTER
• Compare the electrical conductivity of the 4
solid types: ionic, molecular, giant covalent
network and metallic
• Give a detailed explanation for each type
HEAT
1. What is heat?
2. Describe the way it travels
TYPES OF HEAT REACTIONS
• Exothermic = release of heat energy into
surroundings
• Endothermic = absorption of heat energy from
surroundings
PRACTICAL
• Practical 11.1 p138
STARTER
• You have a beaker of water
Describe what
• An endothermic reaction will do to it and why
• An exothermic reaction will do to it and why
WHERE DOES THE ENERGY COME FROM?
• Bond making requires energy = ENDOTHERMIC
• Think about freezing water, what kind of bonds
(attraction) are we making?
• Bond breaking releases energy = EXOTHERMIC
• Think about boiling water, we overcome
intermolecular bonds (attraction) which is
released as heat
• Exothermic = energy to break bonds > energy to
make bonds
• Endothermic = energy to make bonds > energy
to break bonds
COMBUSTION
• All combustion reactions are exothermic
• They release heat
COMBUSTION OF HYDROGEN
2H2 + O2  2H2O
• Bonds broken =
• Bonds made =
• Energy of bonds broken > energy of bonds made
COMBUSTION OF METHANE
CH4 + O2  CO2 + 2H2O
• Bonds broken =
• Bonds made =
ENTHALPY
• Enthalpy is the term for the heat energy in a
substance due to kinetic energy of particles and
potential energy of bonds
• It has the symbol H
• We measure enthalpy change between
REACTANTS and PRODUCTS
• Remember P comes before R in the alphabet
ENERGY DIAGRAMS
•
•
•
•
Exothermic
Hr > Hp
H = Hp – Hr
H = negative
•
•
•
•
Endothermic
Hp > Hr
H = Hp – Hr
H = positive
ACTIVATION ENERGY
HOMEWORK
• Read p138-139
• Do 11A Energetic Reactions on p140