Heat Of Formation Worksheet – 1 Reaction Worksheet enthalpy and calorimetry 1. Calcium carbonate decomposes at high temperature to form carbon dioxide and calcium oxide, calculate the reaction enthalpy. CaCO 3 CO 2 + CaO 2 Chlorine gas reacts with methane to form tetrachloromethane and the reaction enthalpy is calculated. CHCl 2 CCl H 2 3. Under the right conditions, potassium chloride reacts with oxygen to form potassium chlorate: 2 KCl + 3 O 2 2KClO 3 Assuming that the enthalpy of formation of potassium chloride is kj/ mol, the value of the enthalpy of formation of potassium chlorate is kj/mol to measure the reaction enthalpy. Calorimetric Practice 4. Compound A is heated in a bomb calorimeter filled with 2.50 liters of water. If the combustion of moles of this compound causes an increase in the temperature of water by C, what is the molar heat of combustion of compound A? 5. Compound B was heated in a bomb calorimeter filled with 1.50 liters of water. If I burn 50.0 grams of compound B in the calorimeter, the temperature rise of the water in the calorimeter is C. If the heat of combustion of compound B is 2 150 kj/mol, what is the molar mass of compound B? 6. The molar heat of combustion of compound C is 1,250 kj/mol. If I were to burn moles of this compound in a bomb calorimeter in a 2.50 L tank of water, what would be the expected peak?
2 Molar Enthalpy of Solutions INV – Medical Cooling Bags Part 2 1. Explain the difference between heat and temperature. 2. For the compound used in this experiment (Nelson Chemistry 12, p. 347): (a) Calculate the number of moles present in the g sample. (b) Calculate the molar enthalpy (c) Write the thermochemical equation for the dissociation of the compound in water. 3. a) When a substance melts, its temperature or enthalpy increases or decreases. This change in enthalpy is measured as the change in temperature of the water in the calorimeter. Draw a graph showing the enthalpy change when the ionic compound dissolves: (b) From your equation, indicate whether the process is endothermic or exothermic. (c) In your example, is the sign of _H positive or negative? 4. Describe two factors that affect the strength of ionic bonds in a compound. 5. (a) Explain lattice energy and drainage energy. (b) Which factors in part (a) decrease the solubility of ionic compounds? (c) Which material increases in solubility as it ages? 6. To dissolve an ionic solid, an external force must be applied to overcome the attraction that binds its ions together. For example, sodium hydroxide must be heated above 318 degrees Celsius to melt. Despite this high melting point, sodium hydroxide dissolves easily in standard water and decomposes into its ions. a) What energy source is required to dissociate ions in solid sodium hydroxide? b) Why is the resulting sodium hydroxide solution hot? 7. Although ammonium chloride has a melting point of 320 degrees Celsius, it is soluble. Why is ammonium chloride solution cold to the touch? 8. Magnesium oxide MgO and magnesium chloride MgCl 2 are very similar white ionic solids with the following properties: Compound Melting point Solubility MgO 2800 C Insoluble MgCl C Very soluble (a) Give the compound formula for each ion. b) Explain the main differences in physical properties. 9. Consider the following data about chlorides of group 1. These compounds are structurally similar and are composed of + cations and 1 chloride ions. However, they are completely different in terms of lattice energy, hydration energy, and enthalpy of solution. Explain this difference. Lattice energy (kj/mol) Hydration energy (kj/mol) Enthalpy of solution (kj/mol) LiCl NaCl KCI
Heat Of Formation Worksheet
3 Heat of reactionUsing standard values of Η f, calculate the heat of reaction ΔΗ rxn or heat of formation ΔΗ f All answers must include the intermediate reaction steps of the formation of the substance and its manipulation to form the overall reaction. The equation applies to #1-6: ΔHo rxn = ΣnΔHo product ΣnΔHo reactant, e.g. SO2(g) + H20 (1) H2S04(aq) Hkj (1) 1/8 S8 + 02_ SO (2) H2 + 1/2 O2_ H20 (3) H 2 + 1/2 O 2 + 1/8 S 8 _ H 2 SO repeat or modify as needed to add to the original reaction. 1. C 6H 6 (l) + 15/2 O 2 (g) 6 CO 2 (g) + 3 H 2 O (g) HNO 3 (aq) + NO (g) 3 NO 2 (g) cannot be used ) + H20 (1) 3. C2H2 (g) + C2H6 (g) 2 C2H4 (g) 4. Pb02 (s) + CO (g) PbO (s) + CO2 (g) 5. Al2 (S04) 3 ( s ) + 3 H2O (1) Al2O3 (s) + 3 H2SO4 (aq) 6. 3 SO2 (s) + 2 HN03 (aq) + 2 H2O (1) 3 H2SO4 (aq) + 2 NO (g) 7. Calculate Hf.2ClF3 of ClF3 (g) by assuming the following H rxn = kj (g) + 2 NH3 (g) N2 (g) + 6 HF (g) + Cl2 (g) 8. By assuming that H rxn = kj or below, calculate Hf(G)HN02. HN02 (g) + 1/2 O 2 (g) HN03 (aq) 9. Calculate Hf for Fe(CO)5 (g) assuming H rxn = kj. Fe 2 O 3 (s) + 13 CO (g) 2 Fe (CO) 5 (g) + 3 CO 2 (g) 10. Assuming H rxn = kj or less, calculate Hf (s) Fe 3 O 4 . 2 Fe 3 O 4 (s) + CO 2 (g) 3 Fe 2 O 3 (s) + CO (g)
Heat Of Formation Lab
4 Practice tasks from thermochemistry 1. a) Urea (from urine) slowly hydrolyzes in the presence of water to form ammonia and carbon dioxide. If 1 mole of urea reacts with water, what are the standard H, S, and G for the reaction? b) What is the probability of this response? 2. What is G for burning liquid ethanol (C 2 H 5 OH) to CO 2 (g) and H 2 O (g)? Is the reaction spontaneous? 3. Calculate H and S for the following reaction and decide which one of these factors will drive the reaction. N 2(g) + 3 H 2(g) 2 NH 3(g) Use the data below to answer your question: Compound H (kj/mol) S (J/(mol K)) G (kj/( mol K) ) ) CO(NH2)2(aq) H20 (1) C02(g) NH3(g) C2H50H (1) H20 (g) N2 (g) H2 ( G)
5 Additional Enthalpy Questions 1. Construct an enthalpy diagram showing the enthalpy change for the one-step conversion of germanium Ge(s) to GeO2(s) and the two-step conversion—first to GeO(s) oxide and then becomes GeO2( y)). The appropriate thermochemical equation is as follows: Ge(s) + 1/2 O2 (g) GeO(s) H = -255 kj Ge(s) + O2(g) GeO2 (s) H = kj Using this equation, find reaction GeO H value (s) + 1/2 O2 (g) GeO2 (s) 2. Nitric oxide in the air oxidizes to form nitrogen dioxide, a reddish-brown poisonous gas. Construct an accurate enthalpy diagram for this reaction. Use this diagram to explain which nitrogen oxides have strong bonds. 2 NO(g) + O2 (g) 2 NO2 (g) 3. One of the components of protein found in muscles and tendons is an amino acid called glycine, C2H5NO2. Its combustion equation is 4 C2H5NO2 (s) + 9 O2 (g) 8 CO2 (g) + 10 H2O(l) + 2 N2 (g) and its H-comb value is kj/mol. Calculate the Hf of glycine. 4. On Easter Sunday, April 3, 1983, a gas tank near Denver, Colorado spilled nitric acid. The spill was quenched with sodium carbonate. The reaction is 2 HNO3 (aq) + Na2CO3 (s) 2 NaNO3 (aq) + H2O(l) + CO2 (g) (a) Calculate H for this reaction. Hf NaNO3 (aq) is -467 kj/mol, Hf HNO3 (aq) is kj/mol, and Hf Na2CO3 (aq) is kj/mol] (b) About 9.1 x 104 L of -nitric acid was sprayed. Given a molarity of 15.4 M, how much sodium carbonate is needed and how much heat is released for complete reduction. (c) According to the Denver Post of April 4, 1983, authorities were concerned
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