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Unit 1 – Thermochemistry General Outcomes: 1.Determine and interpret energy changes in chemical reactions 2.Explain and communicate energy changes in chemical.

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Presentation on theme: "Unit 1 – Thermochemistry General Outcomes: 1.Determine and interpret energy changes in chemical reactions 2.Explain and communicate energy changes in chemical."— Presentation transcript:

1 Unit 1 – Thermochemistry General Outcomes: 1.Determine and interpret energy changes in chemical reactions 2.Explain and communicate energy changes in chemical reactions

2  Enthalpy of formation  Enthalpy of reaction  ΔH notation  Hess’ Law  Molar enthalpy  Energy diagrams  Activation Energy  Catalysts  Calorimetry  Fuels and Energy Efficiency

3  the potential to do work.  examples of energy changes: - chemical energy in food to motion - solar energy to power - geothermal energy to heat - nuclear energy to power, heat, motion

4  Thermodynamics: study of energy changes in systems  Thermochemistry –study of energy changes involved in physical and chemical changes.

5 First Law - Energy can be neither created nor destroyed, it simply changes forms. E system = -E surroundings Second Law – In any energy conversion, energy is always lost in the form of heat.

6  We can observe the effect it has on our surroundings.  Energy systems either release energy to the surroundings or absorb energy from the surroundings.  Universe = System + Surroundings

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8  Open systems – matter and energy move freely in / out.  Closed systems – only energy moves in / out.  Isolated system – neither matter nor energy moves in / out.

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10 Calculating Thermal Energy

11 1. Q =quantity of heat flowing in / out of that substance, measured as energy in units of joules (J) or kilojoules (kJ) 2. m-mass of substance undergoing the change measured in units of grams (g) or kilograms (kg) 3. c=heat capacity -heat required to change the temp of 1 g of substance by 1 o C

12 1. Many hot water heaters use the combustion of natural gas to heat the water in the tank. When 150 L of water at 10 o C is heated to 65 o C, how much energy flows into the water?

13 2. A solid substance has a mass of g. It is cooled by 25.0 o C, and loses kJ of heat. What is the specific heat capacity and the identity of the substance?

14 3. If a copper pot weighing kg is heated with kJ of energy, what is the expected temperature change?

15  Energy from the sun is stored in the bonds of chemical substances such as fossil fuels and hydrocarbons.

16  Solar energy is captured by plants during photosynthesis.  Living tissues from plants and animals become buried. Instead of decaying, these compounds form hydrocarbons or fossil fuels.  The energy from fossil fuels is released during combustion reactions and converted into heat.

17  Photosynthesis is endothermic: 6CO 2 (g) + 6H 2 O(l) + energy  C 6 H 12 O 6 (s) + 6O 2 (g)  Cellular Respiration is exothermic: C 6 H 12 O 6 (s) + 6O 2 (g)  6CO 2 (g) + 6H 2 O(l) + energy  Combustion is exothermic: CH 4 (g) + 2 O 2 (g)  CO 2 (g) + 2 H 2 O(g) + energy

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19  There are two types of energy that matter may possess: 1. Kinetic energy – the energy of motion 2. Potential energy – the energy of position

20  faster the particle is moving, the greater the kinetic energy.  Can be found in three types: ◦ Translational ◦ Rotational ◦ Vibrational

21  E k measured indirectly by measuring the temperature of a system.  is proportional to the amount of heat a system holds.

22  Stored energy found in the bonds and inter-molecular forces of molecules  Changes in potential energy include phase changes, chemical reactions and nuclear reactions

23  Are changes in potential energy  energy is required to break bonds and the energy is released when new bonds are formed.  chemical reactions:micro/macro chemical reactions:micro/macro

24  enthalpy describes the total amount of energy a system has.  Enthalpy Change (ΔH = kJ) refers to how much the total energy of a system increases or decreases during a chemical reaction.  Molar enthalpy (ΔH = kJ/mol) describes the amount of enthalpy change per mole of substance.

25  Endothermic reaction – less energy is released in forming bonds than was required to break bonds.  (+ΔH)  Surrounding temperature decreases  Exothermic reaction – more energy is released in making bonds than is required to break them.  (-ΔH)  Surrounding temperature increases

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27  H = change in enthalpy (kJ) H = molar enthalpy kJ/mol n = moles n=m/M

28 1. Hydrogen and oxygen gas react to produce g of water vapor. If the molar enthalpy of reaction is kJ/mol for water, what is the enthalpy change?

29 2. The molar enthalpy of combustion for ethanol is kJ/mol. What mass of methanol must be burned to generate 2.34 x 10 4 kJ of energy?

30 3. What is the molar enthalpy of combustion if a 10.0 g sample of pure acetic acid is burned in oxygen and produces kJ of energy?

31 1. Molar enthalpy of a specific reaction relative to one species in the reaction. 2H 2(g) + O 2(g)  2H 2 O (g) H: kJ/mol H 2 O 2. Enthalpy change for a balanced reaction equation. 2H 2(g) + O 2(g)  2H 2 O (g) ∆H: kJ

32 3. Including the energy value as part of the balanced equation. 2H 2 (g) + O 2 (g)  2H 2 O(g) kJ 2C(g) + 2H 2 (g) kJ  C 2 H 4 (g) 4. Drawing a potential energy diagram for the reaction.

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34  used to determine energy changes during physical or chemical processes  calorimeter : ideally an isolated system Energy in Chemical Reactions - Learning Activit - Flash Player Installation

35  All components of the calorimeter are included in the total energy change.  Mathematically, calorimetry may be described as: Heat lost = heat gained (* remember heat lost is expressed as a negative value)

36  used for reactions in aqueous solution  can calculate the heat change in the water and use to determine enthalpy change  P 353 lists assumptions made when using a simple calorimeter

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38 mL of 0.300mol/L CuSO 4 (aq) is mixed with 50.00mL of NaOH(aq). The initial temperature of both solutions is o C and the highest temperature recorded after mixing is o C. a.Determine the enthalpy change for the system b.Determine the molar enthalpy change for CuSO 4 c.Write the thermochemical equation.

39 2. Barium chloride and sodium sulfate react to produce a precipitate of barium sulfate. When mol of precipitate is formed the temperature of 3.00 kg of water is raised from to o C. Calculate the molar enthalpy of reaction for the production of barium sulphate.

40  used for combustion reactions  total energy change of the calorimeter includes changes in the container itself, the water, the thermometer and the stirrer.

41  bomb calorimeters may report a heat capacity for the entire calorimeter system. (C measured in J/ o C)  Q = C  T

42 1. A bomb calorimeter has a heat capacity of 40.00kJ/ o C. Complete combustion of 1.00g of hydrogen causes the temperature of the calorimeter to increase by 3.54 o C. What is the molar enthalpy of combustion from this evidence?

43 2. When 1.00 g of propane is burned, about 2.36 J of heat is given off. What mass of water at 50.0 o C can be heated to 80 o C when 4.00 mol of propane is burned?

44 3. A strip of magnesium metal having a mass of 1.22 g is placed in 100 mL of 1.00 mol/L HCl (aq) in a metal can with a heat capacity of 562 J/ o C. After the reaction, the temperature increased from 23.0 o C to 45.5 o C. Assuming the solution in the calorimeter has the same heat capacity as water, determine the heat of reaction per mole of magnesium.


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