Chapter 5 Thermochemistry PDF

Lecture Handout Chapter 5 Thermochemistry CHE 103 The First Law of Thermodynamics – Movement of Heat What is energy? What is the First Law of Thermodynamics? How does heat move in an isolated system? Lecture Handout Chapter 5 Thermochemistr...

Lecture Handout Chapter 5 Thermochemistry CHE 103 The First Law of Thermodynamics – Movement of Heat What is energy? What is the First Law of Thermodynamics? How does heat move in an isolated system? Lecture Handout Chapter 5 Thermochemistry CHE 103 Thermochemistry and Chemical Reactions - Enthalpy What is enthalpy? What is the relationship between enthalpy and chemical reactions? Energy Energy 17 Thermochemistry Introduction Summary For the combustion of octane: Potential Energy 2 C8H18 (l) + 25 O2 (g) → 16 CO2 (g) + 18 H2O (l) Which of the following releases energy? a) breaking the bonds of the reactants Distance Between Atoms b) forming the bonds of the products Lecture Handout Chapter 5 Thermochemistry CHE 103 Heat Transfer Application: Solving for q How much energy is required to heat a 125 g piece of zinc from 23 °C to 125 °C? The specific heat of zinc is 0.390 J/g ºC How much energy is required to cool a 100. g piece of titanium from 125 °C to 4 °C? The specific heat of titanium is 0.720 J/g ºC Three separate beakers contain 250. g of the following liquids at 23ºC: water; ethanol; and methanol. Which of the liquids will require the most energy to reach their boiling point? a) water (4.184 J/g ºC, BP 100 ºC) b) ethanol (2.46 J/g ºC, 78.4 ºC) d) methanol (2.53 J/g ºC, BP 64.7 ºC) Lecture Handout Chapter 5 Thermochemistry CHE 103 Heat Transfer Application: qsys vs. qsurr, Solving for C 65.39 g of aluminum pellets are heated to 80.0 ºC. They are placed into 500. g of water at room temperature (25.0 ºC). When thermal equilibrium is reached the temperature of the mixture is 26.5 ºC. What is the specific heat of aluminum? The specific heat of water is 4.184 J/g ºC. 105.09 g of nickel pellets are heated to 80.0 ºC. They are placed into 500. g of water at room temperature (25.0 ºC). When thermal equilibrium is reached the temperature of the mixture is 26.2 ºC. What is the specific heat of nickel? The specific heat of water is 4.184 J/g ºC. Lecture Handout Chapter 5 Thermochemistry CHE 103 Measuring Energy and Enthalpy – Calorimetry Draw a diagram for the two main types of calorimetry. What heat exchanges are expected to take place? Enthalpy Application: Calculating Tf Calculate the final solution temperature for the following dissolution reactions: 10.0 g of NaNO3 into 250. g of 25 °C water (NaNO3 84.99 g/mol; ΔrH° = 20.5 kJ/mol; Csoln = 4.22 J/g ºC) 10.0 g of NaOH into 250. g of 25 °C water (NaNO3 39.99 g/mol; ΔrH° = –44.5 kJ/mol; Csoln = 4.22 J/g ºC) Lecture Handout Chapter 5 Thermochemistry CHE 103 Measuring Enthalpy – Constant Pressure Calorimetry The acid-base reaction between aqueous ammonia and aqueous acetic acid is conducted in a coffee cup calorimeter. 50.0 mL of 0.150 M ammonia is mixed with 50.0 mL of 0.200 M acetic acid. Each reactant is initially at 21.6 ºC, and after reaction the temperature in the calorimeter is 22.5 ºC. What is the enthalpy of neutralization for the reaction? Assume a solution density of 1.00 g/mL and a specific heat of 4.22 J/g ºC. The redox reaction between aqueous nickel(II) nitrate and copper metal is conducted in a coffee cup calorimeter to produce copper(II) nitrate and nickel metal. 10.0 g of copper metal is placed into 50.0 mL of 0.500 M nickel(II) nitrate. Each reactant is initially at 21.3 ºC, and after reaction the temperature is 20.6 ºC. What is the enthalpy of reaction? Assume a solution density of 1.00 g/mL and a solution specific heat of 4.22 J/g ºC. Lecture Handout Chapter 5 Thermochemistry CHE 103 Measuring Enthalpy – Constant Volume Calorimetry 3.50 g of FAME biofuel (298.5 g/mol) is combusted in a bomb calorimeter. The bomb calorimeter contains 1.00 kg of water, and the bomb/water rises from 25.5 ºC to 31.6 ºC after combustion. The bomb has a heat capacity of 837 J/ºC, and water has a heat capacity of 4.184 J/g ºC. What is the enthalpy of combustion for biofuel? A 2.50 g sample of powder was combusted in a bomb calorimeter in an excess of oxygen. The temperature of the calorimeter reached 32.73 °C, and prior to the combustion was 23.00 °C. The specific heat of the bomb is 837 J/°C, and the water reservoir was filled with 250. g of distilled water. What is the enthalpy (in kJ/g) of combustion for the powder? Lecture Handout Chapter 5 Thermochemistry CHE 103 Predicting Reaction Enthalpy: What is a “State Function”? Energy Hess’s Law: Standard Reaction Enthalpy Hess’s Law: Summation of stepwise reactions for overall reaction: What is the Enthalpy of Reaction for the following reaction: 2 S (g) + 3 O2 (g) → 2 SO3 (g) ΔrHº = ??? Using the provided reaction information: S (g) + O2 (g) → SO2 (g) ΔrHº = -297 kJ/mol 2 SO3 (g) → 2 SO2 (g) + O2 (g) ΔrHº = +198 kJ/mol Lecture Handout Chapter 5 Thermochemistry CHE 103 What is the Enthalpy of Reaction for the following reaction: W (s) + C (s) → WC (s) ΔrHº = ??? Using the provided reaction information: 2 W (s) + 3 O2 (g) → 2 WO3 (s) ΔrHº = -1681 kJ/mol C (s) + O2 (g) → CO2 (g) ΔrHº = -394 kJ/mol 2 WC (s) + 5 O2 (g) → 2 WO3 (s) + 2 CO2 (g) ΔrHº = -2392 kJ/mol Hess’s Law: Formation Reactions Hess’s Law: Summation of formation reactions for overall reaction: Use enthalpy of formation to determine the standard reaction enthalpy for the reaction of calcium oxide with water. CaO (g) + H2O (l) → Ca(OH)2 (s); ∆rH = ??? Ca (s) + ½ O2 → CaO (s); ∆fH = –635.1 kJ/mol H2 (g) + ½ O2 (g) → H2O (l); ∆fH = –285.8 kJ/mol Ca (s) + H2 (g) + O2 (g) → Ca(OH)2 (s); ∆fH = –986.1 kJ/mol Lecture Handout Chapter 5 Thermochemistry CHE 103 Determine the overall reaction enthalpy for the combustion of naphthalene. C10H8 (g) + 12 O2 (g) → 10 CO2 (g) + 4 H2O (g) C10H8 (g) ∆Hfº = 77.7 kJ/mol; O2 (g) ∆Hfº = 0 kJ/mol; CO2 (g) ∆Hfº = -394 kJ/mol; H2O (g) ∆Hfº = -242 kJ/mol