DP-SL STANDARD J & DP-HL STANDAND K
SEMINARS: CHAPTER 5: ENERGIES/THERMOCHEMISTRY
LG (a) Define the terms endothermic reactions, exothermic reactions and standard enthalpy changes of reactions (ΔH)
DEFINE:
Endothermic reactions
Exothermic reactions
ΔH
LG(b) Explain what is meant by system and surroundings and apply reactions as endothermic or exothermic in terms
of energy lost or gained by the system to/from the surroundings
In your own words, explain what is meant by system and surrounding:
Is the bonds breaking and forming in a reaction considered the system or surroundings? Explain
Is the water in an aqueous solution considered the system or surroundings ? Explain
Is the calorimeter a reaction that a reaction takes place in considered the system or surroundings ? Explain
Draw an arrow to represent how the energy flows in an endothermic and exothermic reaction
Endothermic
Exothermic
Surroundings
Surroundings
System
System
LG (c) Formulate if various types of reactions are endothermic or exothermic
LG( d) Apply the relationship between temperature change, enthalpy change and the classification of a reaction as
endothermic or exothermic.
Judge the following reactions as either endothermic or exothermic and sign the correct sign ( + or -) to ΔH
The combustion of ethane: 2C2H6 + 7O2 4 CO2 + 6H2O
ΔH
The reaction in a cold pack used in sports injuries: NH4Cl + H2O HCl + NH4OH ΔH
The neutralization of hydrochloric acid with sodium hydroxide: HCl + NaOH  H2O + NaCl ΔH
The reaction in a hot pack used in sports injuries: 4Fe + 3O2  2 Fe2O3
ΔH
LG (e) Deduce, from an enthalpy level diagram, the relative stabilities of reactants and products and the sign of the
enthalpy change for the reaction.
DIAGRAM C
Label the diagrams A & B as either endothermic or exothermic and EXPLAIN
DIAGRAM A
DIAGRAM B
reactants_
products
products
H2 + O2
H2O2
reactants
EXTENT OF REACTION
H2O + ½ O2
____________________
Reaction
EXPLAIN:
______________________
Reaction
The most stable state is where all energy has been released. When going to a more stable state, energy will be released,
and when going to a less stable state, energy will be gained (from the surroundings). On an enthalpy level diagram,
higher positions will be less stable (with more internal energy) therefore, if the product is lower, heat is released (more
stable, ΔH is -ve) but if it is higher, heat is gained (less stable, ΔH is +ve).
USING THE INFORMATION IN THE PARAGRAPH ABOVE AND DIAGRAM C ON THE LAST PAGE ,DETERMINE HOW STABLE
THE FOLLOWING REACTIONS ARE(LABEL AS STABLE OR UNSTABLE)
H2 + O2  H2O2 __________________________
H2O2  H2 + O2 __________________________
H2 + O2  H2O + ½ O2 _______________________
H2O + ½ O2  H2 + O2 _______________________
H2O2  H2O + ½ O2 ________________________
H2O + ½ O2  H2O2 _______________________
LG(f) Calculate the heat energy change when the temperature of a pure substance changes
DO EXERCISES
DP-SL #5,6,7 PAGE 101,102,104
DP-HL #5,6&7 PAGE 164,165, & 167
DESIGN AND CARRY OUT AN EXPERIMENT AND THE CALCULATIONS TO FIND THE SPECIFIC HEAT CAPACITY OF AN
ALUMINUM CYLINDER.
MATERIALS: Coffee cup calorimeter, thermometer, aluminum cylinder(will be heated prior to lab, but you will need to
determine the initial temperature of the metal from the water bath it is heated in) and room temperature water
LG(h) Formulate the equations and calculate the enthalpy change of a reaction that is the sum of two or three
reactions with known enthalpy changes.
DO EXERCISES
DP-SL #8,9,10,11 PAGES 106,108,109
DP-HL # 8,9,PAGES 170,172
LG(i) Calculate average bond enthalpy and determine if the reaction if endothermic or exothermic.
DO EXERCISES
DP-SL #12,13,14,15 PAGES 111,112
DP-HL #10,11,12,13,14,15 PAGES 172,174
LAB: LG(g) Design a suitable experimental procedure for measuring the heat energy changes of reactions