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Chapter 10 – Energy

Chapter 10 – Energy. What is Energy? Temperature & Heat Measuring Energy Changes – Specific Heat Capacity First Law of Thermodynamics Enthalpy Hess’ Law Second Law of Thermodynamics – Entropy Fuels for the Modern World. Example 1. A brownie contains 320 Calories. Express

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Chapter 10 – Energy

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  1. Chapter 10 – Energy • What is Energy? • Temperature & Heat • Measuring Energy Changes – Specific Heat Capacity • First Law of Thermodynamics • Enthalpy • Hess’ Law • Second Law of Thermodynamics – Entropy • Fuels for the Modern World

  2. Example 1 A brownie contains 320 Calories. Express this in calories and in Joules.

  3. Example 2 How much energy is required to heat 10.0 g of iron from 25.0°C to 100.0°C? The specific heat capacity of iron is 0.45 J/g°C.

  4. Example 3 A 19.6 g sample of an unknown metal was heated from 22.0°C to 53.8°C by the addition of 558.6 J of energy. Find the specific heat capacity of the metal. Refer to the table of specific heat capacities in your textbook to predict what metal this might be.

  5. Example 4 How much energy (in joules) is needed to heat a cup of water for coffee?  Assume the following: the cup holds 250 mL of water the density of water is 1.00 g/mL the water is initially at 19°C the ideal temperature for brewing coffee is 97°C Answer: 81.6 x 103 J

  6. Example 5 A system releases 255 calories of heat and does 428 calories of work. What is the change in internal energy of this system? Answer: -683 calories

  7. Example 6 The enthalpy of the reaction CH4 (g) + 2O2 (g) CO2 (g) + 2 H2O (g)is -890.4 kJ/mol. What is the enthalpy for the reaction below? 2 CO2 (g) + 4 H2O (g) 2 CH4 (g) + 4 O2 (g)

  8. Example 7 How much heat is released when 2.50 g of N2 reacts with excess H2 to form NH3 (g)? N2 (g)  +  3 H2 (g)    2 NH3 (g) DH° = -91.8 kJ per mole of N2 consumed. Answer: 8.20 kJ are released

  9. Example 8 Methane, CH4, is natural gas, a commonly used fuel. How much methane must be burned to release 100.0 kJ of energy? Assume the enthalpy change for the combustion of 1 mole of methane is -890.4 kJ.

  10. Example 9 Which provides more energy, burning 1.00 g of gasoline (C8H18) or 1.00 g of ethanol (C2H5OH)? C8H18(l) + 25/2 O2(g)  8 CO2(g) + 9 H2O(g) DH = -5468kJ per mole of gasoline burned C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(g) DH = -1367kJ per mole of ethanol burned

  11. Example 10 Given the following reactions: 2SO2 (g) + O2 (g)  2SO3 (g); DH1 = -196kJ 2S (s) + 3O2 (g)  2SO3 (g); DH2 = -790 kJ Calculate the heat of reaction for S (s) + O2 (g)  SO2 (g)

  12. Example 11 Given the following reactions: H2S (g) + 3/2 O2(g)  H2O(l) + SO2(g); DH1 = -563 kJ CS2 (l) + 3O2(g)  CO2(g) + 2SO2(g); DH2 = -1075 kJ Calculate DHrxn for this reaction: CS2(l) + 2 H2O(l)  2 H2S(g) + CO2(g)

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