Y11 Chemistry T3 Extensive Notes

Module Worksheet Solutions

- https://docs.google.com/document/d/
1tDiR6HgYL241alWeukmN3dUDuDKZ3M1XeEFE78SJdkA/edit (2023 Y11 Chem
Syllabus Notes)
- CHEM Term 1 Document; CHEM Term 2 Document

PRE 1.11 Physical and Chemical Changes 😊

PRE 2.8 Experiment: Reactions of Metals 😊

PRE 3.19 Experiment: Preparing and Diluting Solutions 😡

PRE 4.11 Energy in Chemical Reactions ✨

PRE 4.14 Experiment: Effect of Catalysts and Particle Size on Rate of Reaction

PRE 4.15 Reaction Rates 😐

PRE 4.16 Heat of Combustion Problems 😊




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,20.07 Energy Changes in Chemical Reactions

- https://docs.google.com/presentation/d/1YM-o_kfPZq_CuCLx5y8qCt52HZ-
aRqX2zEnOhTUr28Y/edit#slide=id.p3 (Presentation)

Heat Capacity
- Ability to store heat
- Measured in joules
- Usually refers to the amt. of heat energy required to
change the substance temperature by one degree
- Units are J g-1 K-1

Energy and Heat Transfer
- Absolute values are impossible to measure so
scientists just measure differences in energy
- Heat is giving the symbol “q”
- We measure changes in “local surroundings” and
ensure/assume that no energy is transferred to the rest of the universe

q = quantity of heat (absorbed or released) in Joules (J)
m = mass in grams (g)
q = mC∆T C = specific heat capacity (J g-1 K-1)
ΔT = Tf – Ti = final temperature – initial temperature (oC or K)
- If ∆T > 0 (and thus q > 0, positive), the object has gained heat
- If ∆T < 0 (and thus q < 0, negative), the object has lost heat

Specific Heat Capacity at 298.15 K Energy Unit Conversion (Joules)




1 MJ = 1,000 kJ = 100,000 J = 1.0 x 106 J




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,Chemical Reactions
- (5) Some indicators: permanent colour change, odour, gas product, formation of
precipitate, release or absorption of energy

BOND BREAKING REQUIRES
ENERGY
Energy is transferred from
particle to particle during
collision

BOND FORMING RELEASES
ENERGY
Also increases kinetic energy of
particles

Enthalpy (Heat Content, H)
- Total heat content of system = The sum of the kinetic and potential energies of 1 mole of
the particles that comprise the material.
- It indicates the stored chemical energy in a system at a given pressure and temperature.
- We can only measure differences in enthalpy

Enthalpy Change (ΔH)
- Measured in kJ/mol
- ΔH = enthalpy of products (energy needed to break bonds) - enthalpy of reactants
(energy released when new bonds are formed)
- Exothermic reactions: ΔH < 0
- Endothermic reactions: ΔH > 0
- *ΔH is the HEAT ABSORBED going from reactants to products

Thermochemical equation is a balanced stoichiometric chemical equation that includes the
enthalpy change, ΔH

Energy Profile for Exothermic and Endothermic Reactions




- Exothermic reactions: e.g. heat of combustion, and heat of neutralisation
- Endothermic reactions: e.g. photosynthesis, and electrolysis (decomposition of water)



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, Enthalpy Diagrams for Chemical Reactions




Measuring ΔH: Bomb Calorimeter
Calorimeter is an apparatus used to measure heat changes during chemical reaction or a
change of state. Calorimetry is the measure of heat changes in systems.
- Reaction vessel surrounded by an insulated container enclosing a known mass of water
- By using water’s specific heat capacity and a calorimeter, the heat energy (enthalpy)
released and absorbed from chemical reactions can be readily measured.

- Cheaper calorimeter can be made using styrofoam cup (low heat capacity, low heat
loss)
- When determining enthalpy changes, heat should not be gained or lost to the
surroundings. To prevent heat transfer, a calorimeter should provide insulation.
- Limitations: Read pg. 274 of Jacaranda textbook (insulation, accurate measurement,
absorption of heat into larger mass surrounding water, thermal capacity, thermal
conductivity, etc)




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