3.1: Know that Chemical Reacts in Which Heat Energy is Given Out are Described as Exothermic, and those in Which Heat Energy is Taken In are Described as Endothermic

EXOTHERMIC	ENDOTHERMIC
Diagram showing Enthalpy Change during an Exothermic Reaction	Diagram showing Enthalpy Change during an Endothermic Reaction
DEFINITION: Reaction in which energy is given out to surrounding, decreasing energy level (temperature increases)	DEFINITION: Reaction in which energy is taken in from surrounding, increasing energy level (temperature decreases)
EXAMPLE: Burning Neutralisation Reaction between Water and Calcium Oxide	EXAMPLE: Electrolysis Thermal decomposition of Copper (II) Carbonate Reaction between Acetic Acid and Sodium Carbonate

3.2: Describe Simple Calorimetry Experiments for Reactions such as Combustion, Displacement, Dissolving and Neutralisation

CALORIMETRY EXPERIMENT: Method to Measure heat transfer

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CALORIMETRY EXPERIMENT FOR COMBUSTION:

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CALORIMETRY EXPERIMENT - COMBUSTION

Diagram showing the Calorimetry Experiment for Combustion

METHOD: Using a measuring cylinder, measure 100 cm3 of Water into a Copper can (copper provides efficient heat insulation) Measure and record the initial temperature of Water Filling the spirit burner with test substance, measure and record its mass Place burner under Copper can and light the wick Constantly stir the Water and continue heating until temperature rises by about 20 - 30°C, then B\blow out the flame Measure and record the highest temperature of Water Measure and record the final mass of burner and remaining Alcohol

CALCULATION: Rise in Temperature of Water    =    Final Temperature - Initial Temperature Mass of Alcohol Burnt     =    Initial mass - Final mass Enthalpy Change:

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CALORIMETRY EXPERIMENT FOR DISPLACEMENT, DISSOLVING AND NEUTRALISATION:

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CALORIMETRY EXPERIMENT - DISPLACEMENT, DISSOLVING AND NEUTRALISATION

Diagram showing Calorimetry Experiment for Displacement, Dissolving and Neutralisation

METHOD: Using a measuring cylinder, measure 25 cm3 of Solution 1 into a Polystyrene cup Measure and record the temperature of Solution 1 Add measured amount of reactant (solid for dissolving, solution 2 for displacement and neutralisation) into the Polystyrene cup and stir the mixture Measure and record the highest temperature reached by mixture

CALCULATION: Rise in Temperature    =    Final Temperature - Initial Temperature Mass of Solution  =  Solution 1 + Solution 2  OR Solution 1 if solid is dissolved Enthalpy Change: *If Water is not used, this is replaced by the mass or volume of other solutions

3.3: Calculate the Heat Energy Change from a Measured Temperature Change Using the Expression Q = mc△T

HEAT ENERGY CHANGE:

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Data from calorimetry experiment can be used to calculate the heat energy change of a reaction:

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EQUATION:

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* m = Mass of Water or volume of Water

*If Water is not used, this is replaced by mass or volume of other solutions

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Example:

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Energy from burning 0.5 g of Propane was transferred to 100 cm3 of Water to raise its temperature by 20°C. Calculate the heat energy change (in KJ)

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Mass of Water =     100 cm3 Heat Capacity of Water =     4.2 j / g Temperature Rise     =     20°C Energy Transferred     =     100    x    4.2    x    20    =    8400 J *1000 J = 1 KJ So 8400 J   =  8.4 KJ                                                                                       Energy Transferred = 8.4 KJ

3.4: Calculate the Molar Enthalpy Change (△H) from the Heat Energy Change, Q

MOLAR ENTHALPY CHANGE:

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Data from a Calorimetry Experiment can be used to calculate the molar enthalpy change of reaction:

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EQUATION:

* m = Mass of Water or Volume of Water

*If Water is not used, this is replaced by the mass or volume of other solutions

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Example:

Energy from burning 0.5 g of Propane was transferred to 100 cm3 of Water to raise its temperature by 20°C. Calculate the molar enthalpy change (in KJ / Mol)

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Mass of Water =     100 cm3 Heat Capacity of Water =     4.2 j / g Temperature Rise     =     20°C Energy Transferred     =     100    x    4.2    x    20    =    8400 J *1000 J = 1 KJ So 8400 J   =  8.4 KJ Mr of Propane = 44 Moles of Propane Burned     =     0.5     ÷     44     =     0.01136 Molar Enthalpy Change     =     8.4     ÷     0.01136     =     739 Reaction is exothermic so enthalpy change needs to be Negative                                                                     Molar Enthalpy Change = - 739 KJ / Mol

3.5C: Draw and Explain Energy Level Diagrams to Represent Exothermic and Endothermic Reactions

EXOTHERMIC	ENDOTHERMIC
Diagram showing the Enthalpy Change during an Exothermic Reaction	Diagram showing the Enthalpy Change during an Endothermic Reaction
DEFINITION: Reaction in which energy is given out to surroundings, decreasing energy level (temperature increases)	DEFINITION: Reaction in which energy is taken in from surroundings, increasing energy level (temperature decreases)
EXPLANATION: During an exothermic reaction, energy is given out to surroundings Therefore, the energy of products will be lower than the energy of reactants, having -△H (this is represented in energy-level diagram above)	EXPLANATION: During an endothermic reaction, energy is taken in from surroundings Therefore, the energy of products will be higher than the energy of reactants, having +△H (this is represented in energy-level diagram above)

3.6C: Know that Bond-Breaking is an Endothermic Process and that Bond-Making is an Exothermic Process

ENDOTHERMIC AND EXOTHERMIC REACTIONS

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Whether reaction is endothermic or exothermic depends on difference between the energy needed to break bonds and the energy released when new bonds form

ENDOTHERMIC:

• If more energy is absorbed than it releases, reaction is Endothermic as more energy is absorbed to break bonds

Diagram showing the Bond-Breaking in an Endothermic Reaction


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EXOTHERMIC:

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• If more energy is released than is absorbed, reaction is exothermic as energy is released when new bonds form

Diagram showing the Bond-Making in an Exothermic Reaction

3.7C: Use Bond Energies to Calculate the Enthalpy Change during a Chemical Reaction

BOND ENERGY: Energy required to break a bond

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METHOD:

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• Add all bond energies for all the bonds in reactant - this is the ‘energy in’
• Add all bond energies for all the bonds in products - this is the ‘energy out’
• Calculate the energy change: energy in - energy out

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EQUATION:

Energy Change     =     Energy In     -     Energy Out

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Example: An Exothermic Reaction

Hydrogen and Chlorine reacts to form Hydrogen Chloride Gas:

H - H   +   Cl - Cl    →    2    x    (H - Cl)

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Table below shows the bond energies relevant to this reaction:

BOND	BOND ENERGY ( KJ / MOLE )
H - H	436
Cl - Cl	243
H - Cl	432

Energy In    =     436     +     243    =    679 KJ / Mole Energy Out     =    2    x    243    =    864 KJ / Mole Energy Change    =    679    -    864    =    -185 KJ / Mole *Energy change is negative, therefore showing that more energy is given out to the surroundings than taken in, indicating that this is an Exothermic Reaction

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Example: An Endothermic Reaction

Hydrogen Bromide Decomposes to Form Hydrogen and Bromine:

2   x   ( H - Br )    →    H - H    +    Br - Br

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Table below shows the bond energies relevant to this reaction:

BOND	BOND ENERGY ( KJ / MOLE )
H - Br	366
H - H	436
Br - Br	193

Energy In    =     2     x     366    =    732 KJ / Mole Energy Out     =    436    +    193    =    629 KJ / Mole Energy Change    =    732    -    629    =    +103 KJ / Mole *Energy change is positive, therefore showing that more energy is taken in from the surroundings than is given out, indicating that this is an Endothermic Reaction