Name Date Class SECTION 16.1 PROPERTIES OF SOLUTIONS

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1 SOLUTIONS Practice Problems In your notebook, solve the following problems. SECTION 16.1 PROPERTIES OF SOLUTIONS 1. The solubility of CO 2 in water at 1.22 atm is 0.54 g/l. What is the solubility of carbon dioxide at 1.86 atm? Assume that temperature is constant. 2. What mass of KCl will produce a saturated solution in g of water at 20 C? The solubility of KCl at 20 C is 34.0 g/100 g H 2O. 3. A saturated solution of silver nitrate is prepared in g of water at 20 C. The solution is then heated to 50.0 C. How much more silver nitrate must now be added to obtain a saturated solution? (Use Table 16.1.) SECTION 16.2 CONCENTRATIONS OF SOLUTIONS 1. Calculate the molarity of each of the following solutions. a mol of NaCl dissolved in 1.6 L of solution b g of potassium nitrate, KNO 3, in enough water to make ml of solution 2. Calculate the number of grams of solute needed to prepare each of the following solutions. a ml of a 3.0M solution of potassium hydroxide, KOH b. 2.0 liters of 2.0M nitric acid, HNO 3, solution 3. What is the molarity of a solution that contains g of sodium nitrate (NaNO 3) in 3.0 liters of solution? 4. You must prepare ml of 0.750M NaBr solution using 2.00M NaBr stock solution. How many milliliters of stock solution should you use? 5. In order to dilute 1.0 L of a 6.00M solution of NaOH to 0.500M solution, how much water must you add? 6. What is the concentration in percent by volume, %(v/v), of the following solutions? a ml of methanol in a total volume of ml b ml of rubbing alcohol (C 3H 7OH) diluted to a volume of ml with water 7. How many grams of solute are needed to prepare each of the following solutions? a L of a 3.00% (m/m) NaCl solution? b L of 5.00% (m/m) KNO 3 solution? Chapter 16 Solutions 407

2 COLLIGATIVE PROPERTIES OF SOLUTIONS Section Review Objectives Identify the three colligative properties of solutions Describe why the vapor pressure, freezing point, and boiling point of a solution differ from those properties of the pure solvent. Vocabulary colligative properties freezing-point depression boiling-point elevation Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. 1 In a solution, the effects of a nonvolatile on the properties of the solvent are called. 2 They include 3 point and vapor pressure, 4 and boiling point. 5 In each case, the magnitude of the effect is 6 proportional to the number of solute molecules or ions present in the 7. Colligative properties are a function of the number of solute 8 in solution. For example, one mole of sodium chloride produces 9 as many particles in solution as one mole of sucrose and, thus, will depress the freezing point of water 10 as much

3 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 11. When added to 1000 g of water, 2 moles of a solute will increase the boiling point by C. 12. One mole of solute A will depress the freezing point of 1000 g of water the same as one mole of solute B. Chapter 16 Solutions Addition of a nonvolatile solute will lower the boiling point of a solvent. 14. Addition of a nonvolatile solute will lower the freezing point of a solvent. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 15. colligative properties a. difference between the freezing point of a solution and the freezing point of the pure solvent 16. freezing-point depression b. pressure exerted by a vapor that is in equilibrium with its liquid in a closed system 17. boiling-point elevation 18. vapor pressure c. difference between the boiling point of a solution and the boiling point of the pure solvent

4 d. properties of solutions that depend only on the number of particles in solution

5 Part D Questions and Problems Answer the following questions in the space provided. 19. How many moles of solute particles are produced by adding one mole of each of the following to water? a. sodium nitrate b. glucose c. aluminum chloride d. potassium iodide 20. An equal number of moles of NaCl and K2CO3 are dissolved in equal volumes of water. Which solution has the higher a. boiling point? b. vapor pressure? c. freezing point? CALCULATIONS INVOLVING COLLIGATIVE PROPERTIES

6 Section Review Objectives Calculate the molality and mole fraction of a solution Describe how the freezing-point depression and boiling-point elevation are related to molality Vocabulary molality (m) mole fraction molal freezing-point depression constant (K f) molal boiling-point elevation constant (K b) Key Equation moles of solute Molality = kilogram of solvent n mole fractions: X = X = A B A B na + nb na + nb where na = moles of solute nb = moles of solvent b = b T K m f = f T K m n Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. Molality is an expression of concentration involving the ratio of 1 particles to 2 particles. Molality is expressed as moles of solute per 3 of solvent. Another expression of concentration is, 4 in which concentrations are expressed as the ratio of moles of solute to the total number of moles of solvent and solute. Each solvent has a characteristic 5 elevation constant and molal freezing-point 6 constant. The elevation in boiling point of a solution can 7 be calculated by multiplying the concentration of the 8 solution by the boiling-point constant of the solvent

7 8. Chapter 16 Solutions 405 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 9. It is possible to calculate the molar mass of a solute if you know the Kb or Kf of a solvent. 10. Molal concentration is the same as molar concentration. 11. The depression in freezing point of a solution is proportional to the molal concentration of solute. 12. The sum of XA and XB for any solution is always 1. Part C Matching Match each description in Column B to the correct term in Column A. Column A 17. molar mass 13. molality 14. mole fraction 15. molal freezing-point depression constant 16. molal boiling-point elevation constant

8 Column B a. a constant for a given solvent equal to the change in boiling point for a 1m solution b. number of moles of solute dissolved in 1 kilogram of solvent c. mass of one mole of a substance d. a constant for a given solvent equal to the change in freezing point for a 1m solution e. ratio of moles of solute in solution to the total number of moles of solute and solvent

9 Part D Problem Solve the following problem in the space provided. Show your work. 18. What is the freezing point of a solution that contains 2.0 mol of CaCl2 in g of water? Kf for water = 1.86 C/m 406 Core Teaching Resources THERMOCHEMISTRY Practice Problems In your notebook, solve the following problems.

10 SECTION 17.1 THE FLOW OF ENERGY HEAT AND WORK Use the three-step problem-solving approach you learned in Chapter How many kilojoules of energy are in a donut that contains Calories? 2. What is the specific heat of a substance that has a mass of 25.0 g and requires calories to raise its temperature by 15.0 C? 3. Suppose g of H2O(s) absorbs J of heat. What is the corresponding temperature change? The specific heat capacity of H2O(s) is 2.1 J/g C. 4. How many joules of heat energy are required to raise the temperature of g of aluminum by C? The specific heat capacity of aluminum is 0.90 J/g C. SECTION 17.2 MEASURING AND EXPRESSING ENTHALPY CHANGES 1. A student mixed 75.0 ml of water containing 0.75 mol HCl at 25 C with 75.0 ml of water containing 0.75 mol of NaOH at 25 C in a foam cup calorimeter. The temperature of the resulting solution increased to 35 C. How much heat in kilojoules was released by this reaction? Cwater = 4.18 J/g ºC 2. Calculate the amount of heat evolved when 15.0 g of Ca(OH)2 forms from the reaction of CaO(s) + H2O(l). CaO(s) + H2O(l) Ca(OH)2(s) ΔH = 65.2 kj 3. Calculate the amount of heat produced when 52.4 g of methane, CH4, burns in an excess of air, according to the following equation. CH4(g) + 2O2(g) CO2(g) + 2H2O(l) ΔH = kj 4. Balance the following equation, then calculate the enthalpy change for the reaction given that the standard heat of combustion of NH3(g) is 226 kj/mol. NH3(g) + O2(g) NO(g) + H2O(g) SECTION 17.3 HEAT IN CHANGES OF STATE 1. Calculate the amount of heat needed to melt 35.0 g of ice at 0 C. Express your answer in kilojoules. 2. Calculate the amount of heat needed to convert g of liquid water at 18 C to steam at C. 3. How much heat (kj) is released when mol NaOH(s) is dissolved in water? H2O( l) + NaOH(s) Na ( aq) + OH ( aq) ΔH soln = kj/mol

11 Chapter 17 Thermochemistry 437

12 4. Calculate the amount of heat needed to convert 96 g of ice at 24 C to water at 28 C. The specific heat capacity of H2O(s) is 2.1 J/g ºC. SECTION 17.4 CALCULATING HEATS OF REACTION 1. What is the standard heat of reaction for the combustion of hydrogen sulfide? Refer to Table 17.4 in your textbook. 2H2S(g) + 3O2(g) 2H2O(g) + 2SO2(g) 2. Calculate the enthalpy change (in kj) for the following reaction. State whether the reaction is exothermic or endothermic. Refer to Table 17.4 in your textbook. CaO(s) + CO2(g) CaCO3(s) 3. What is the enthalpy change for the formation of hydrazine, N2H4(l), from its elements? N2(g) + 2H2(g) N2H4(l) Use the following reactions and enthalpy changes: N2H4(l) + O2(g) N2(g) + 2H2O(l) H = kj H2(g) O2(g) H2O(l) H = kj

13 438 Core Teaching Resources THE FLOW OF ENERGY HEAT AND WORK Section Review Objectives Explain the relationship between energy, heat, and work Distinguish between exothermic and endothermic processes Distinguish between heat capacity and specific heat Vocabulary thermochemistry surroundings exothermic process chemical potential energy law of conservation of energy heat capacity heat endothermic process specific heat system

14 Key Equations and Relationships 1 Calorie = 1 kilocalorie = 1000 calories 1 J = cal and J = 1 cal q heat (joules or calories) C = = m Δ T mass (g) change in temperature ( C) Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. The energy that flows from a warm object to a cool object is called. 1 The energy stored within the structural units of chemical substances is called chemical. 2 The study of heat transfer during chemical reactions and changes of state is called. 3 One of the units used to measure heat flow is the, 4 defined as the amount of heat needed to raise 1 g of water 1 C. The SI unit of heat and energy is the, 5 which is equal to cal. 6 The of a substance is the amount of heat it takes to change the 7 temperature of 1 g of the substance 1 C. Substances like, with low heat capacities, take a shorter time to heat up than substances with high heat 8 capacities, such as

15 Chapter 17 Thermochemistry 429

16 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 9. The joule is the SI unit of force. 10. Endothermic processes absorb heat from the surroundings. 11. The law of conservation of energy states that in a chemical process, energy is sometimes created and sometimes destroyed. 12. A system that loses heat to its surrounding is said to be exothermic, and the value of q is negative. 13. A calorie is defined as the quantity of heat needed to raise the temperature of 1 gram of pure water 1 C. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 14. heat a. a process that absorbs heat from the surroundings 15. exothermic process b. the amount of heat required to change the temperature of an object by exactly 1 C 16. heat capacity c. energy that transfers from one object to another because of a temperature difference between them d. the part of the universe being studied 17. system e. a process that loses heat to the surroundings 18. endothermic process

17 Part D Questions and Problems Answer the following in the space provided. 19. Distinguish among the various forms of energy: chemical potential energy, work, and heat. 20. The temperature of a piece of unknown metal with a mass of 18.0 g increases from 25.0 C to 40 C when the metal absorbs J of heat. What is the specific heat of the unknown metal? Compare your answer to the values listed in Table 17.2 of your textbook. What is the identity of the unknown metal? 430 Core Teaching Resources MEASURING AND EXPRESSING ENTHALPY CHANGES Section Review Objectives Construct equations that show the enthalpy changes for chemical and physical processes Calculate enthalpy changes in chemical and physical processes Vocabulary

18 calorimetry calorimeter enthalpy, (H) thermochemical equation heat of reaction heat of combustion Key Equation sys surr q = Δ H = q = m C Δ T, where T = T T f i Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. 1 A is a device used to measure the absorption or release of heat in chemical and physical processes. For systems at constant pressure, the heat changes that occur are the same as changes in, 2 symbolized as. 3 To measure the enthalpy change for a reaction in aqueous solution, it is 4 5 necessary to measure the and temperatures 6 of the system and the of the water in the system Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 7. When a substance dissolves in water, heat is released. 8. The sign of H is negative for an exothermic reaction. 9. If 129 kj of heat is required to decompose 2 moles of NaHCO3, then 258 kj is required to decompose 4 moles of NaHCO3. Chapter 17 Thermochemistry 431

19 10. The physical state of the reactants and products in a thermochemical reaction are not important when calculating H of the reaction. 11. In endothermic reactions, the potential energy of the product(s) is higher than the potential energy of the reactants. 12. The equation CaO(s) + H2O(l) Ca(OH)2(s) ΔH = 65.2 kj is an example of a thermochemical equation. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 13. enthalpy (H) a. the heat of reaction for the complete burning of 1 mole of a substance 14. heat of combustion b. a chemical equation that includes the enthalpy change (ΔH) 15. thermochemical equation 16. calorimetry 17. bomb calorimeter c. the accurate and precise measurement of heat changes for chemical and physical processes d. an insulated device containing a sealed vessel that is used to measure the heat released during a combustion reaction e. the amount of heat that a system has at a constant pressure

20 Part D Questions and Problems Answer the following in the space provided. 18. When 2 moles of nitric oxide, NO, burn in air to produce 2 moles of nitrogen dioxide, kj of heat is produced. Write a balanced thermochemical equation for this reaction. 19. Calculate the amount of heat produced when 34.8 g of methane, CH4, burns in an excess of oxygen, according to the following equation. CH4(g) + 2O2(g) CO2(g) + 2H2O(l) H = kj 432 Core Teaching Resources HEAT IN CHANGES OF STATE

21 Section Review Objectives Classify, by type, the enthalpy changes that occur during melting, freezing, boiling, and condensing Calculate the enthalpy changes that occur during melting, freezing, boiling, and condensing Explain what thermochemical changes can occur when a solution forms Vocabulary molar heat of fusion molar heat of solidification molar heat of vaporization molar heat of condensation molar heat of solution Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. The heat absorbed by 1 mole of a substance in melting from a solid to a liquid at a constant temperature is called the 1. The heat lost when 1 mole of a liquid solidifies at a constant temperature is called 2 the. The quantity of heat absorbed by a melting 3 solid is to the quantity of heat 4 lost when the liquid solidifies. The heat of fusion for methanol is. When liquids absorb heat at their boiling points, they become vapors. The amount of heat necessary to vaporize one mole of a given liquid is called its. 5 6 is the exact opposite of vaporization. The amount of heat released when one mole of vapor condenses is called its

22 Chapter 17 Thermochemistry 433 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 8. Hfus = ΔHsolid 9. Melting and vaporization are exothermic processes. 10. In order to convert 1 mole of H2O(l) to 1 mol of H2O(g), 40.7 kj must be supplied. 11. When ice melts, the temperature of the ice increases until the entire sample becomes liquid. 12. When ammonium nitrate dissolves in water, the solution gets cold. This is an example of an exothermic reaction. Part C Matching Match each description in Column B to the correct term in Column A. Column A 15. molar heat of vaporization 13. molar heat of fusion 16. ΔHvap 14. molar heat of solidification 17. molar heat of solution

23 Column B a. the heat absorbed by 1 mole of a substance in melting from a solid to a liquid b. the amount of heat necessary to vaporize 1 mole of a liquid c. = ΔHcond d. the heat change caused by dissolution of 1 mole of substance e. the heat lost when 1 mole of a liquid solidifies at a constant temperature

24 Part D Questions and Problems Answer the following in the space provided. 18. State whether the following physical and chemical changes are endothermic or exothermic. a. melting d. fusion b. vaporization e. freezing c. condensation f. combustion 19. How much heat is absorbed when 28.3 g of H2O(s) at 0 C is converted to liquid at 0 C? 20. How much heat is absorbed when 5.53 mol of NH4NO3 solid is dissolved in water? (ΔHsoln = 25.7 kj/mol) 434 Core Teaching Resources CALCULATING HEATS OF REACTION Section Review Objectives Apply Hess s law of heat summation to find enthalpy changes for chemical and physical processes Calculate enthalpy changes using standard heats of formation

25 Vocabulary Hess s law of heat summation standard heat of formation Key Equation f f Δ H = Δ H (products) Δ H (reactants) Part A Completion Use this completion exercise to check your understanding of the concepts and terms that are introduced in this section. Each blank can be completed with a term, short phrase, or number. Hess s law of heat summation states that for a chemical equation that can be written as the 1 of two or more steps, the 2 change for the final equation equals the sum of the enthalpy changes for the individual steps. Hess s law makes it possible to measure the heat of a 3 reaction. When a reaction is reversed, the sign 4 of H must be. Sometimes it is hard to measure the heat for a reaction. In such cases, the 5 is used to calculate heats of reaction at standard conditions. The standard heat of formation of a compound is the 6 in enthalpy that accompanies the formation 7 of mole of a compound from its elements. The symbol used 8 for standard heat of formation is. The standard heat of 9 formation of a free element in its standard state is. The 10 standard heat of reaction is determined by the of all 0 ΔH f the reactants from the 0 ΔH f of all the products. Chapter 17 Thermochemistry 435

26 Part B True-False Classify each of these statements as always true, AT; sometimes true, ST; or never true, NT. 11. The standard heat of formation for a substance is determined at 100 C. 12. Hess s law of heat summation is not related to the law of conservation of energy. 13. When using Hess s law of heat summation, intermediate reactions are summed and terms are canceled, as in algebra, to arrive at a final equation. 14. The 0 ΔH f for I2(g) is zero. 15. The 0 ΔH f for H2O(l) and H2O(s) are the same. Part C Matching Match each description in Column B to the correct term in Column A. Column A Column B 16. standard heat of formation a. symbol for the standard heat of formation 17. Hess s law of heat summation b. the change in enthalpy that accompanies the formation of 1 mole of a compound from its elements ΔH f c. in going from a particular set of reactants to a particular set of products, the enthalpy change is the same whether the reaction takes place in one step or in a series of steps 19. H 0 for Br2(g) Br2(l) d kj 20. zero e. 0 ΔH f of Cl2(g)

27 Part D Questions and Problems Answer the following in the space provided. 21. Determine the heat of reaction for the following reaction. CuO(s) + H2(g) Cu(s) + H2O(g) Use the following thermochemical equations. 1) CuO( s ) Cu( s ) + 1 O ( g ) H =155 kj 2 2) H O( g ) H ( g ) + 1 O ( g ) Δ H = 242 kj Calculate the change in enthalpy for the following reaction using standard heats of formation. (Refer to Table 17.4 in your textbook.) Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g) 436 Core Teaching Resources