Miss Adams Chemistry

Transcription

1 Miss Adams Chemistry

2 Homework #1: Energy Conversions Solve the following problems using the conversions listed below. Report your answer with the correct units. Conversions: 1 calorie = 4.18 joules 1 Calorie = 1000 calories 1kilocalorie= 1 Calorie (food) 1. How many calories are in joules? 2. How many kilojoules are in calories? 3. A fruit and oatmeal bar supplies 142 Calories (food calories). How much energy is this in calories? 4. A healthy breakfast supplies 230 Calories (food calories). How much energy is this in joules? 5. A chemical reaction releases 86.5 kj. How many calories is this? 2

3 HW #2: Worksheet on Energy Changes (Joules) 1. A g piece of iron absorbs joules of heat energy, and its temperature changes from 25 C to 175 C. Calculate the specific heat capacity of iron. 2. How many joules of heat are needed to raise the temperature of 10.0 g of aluminum from 22 C to 55 C, if the specific heat of aluminum is 0.90 J/g C? 3. Calculate the specific heat of a piece of wood if g of the wood absorbs joules of heat, and its temperature changes from 32 C to 57 C grams of 4.0 C water are heated until its temperature is 37 C. If the specific heat of water is 4.18 J/g C, calculate the amount of heat energy in Joules needed to cause this rise in temperature. 5. A nugget of pure gold absorbs 276 J of heat. If the specific heat of gold is J/g C, and the temperature rises by 475 C, what is the mass of the gold? 6. To what temperature will a 50.0 g piece of glass raise if it absorbs 5275 joules of heat and its specific heat is 0.50 J/g C? The initial temperature of the glass is 20.0 C. Hint: calculate change in temp. first from mass and specific heat! 3

4 HW #3: Worksheet on Energy Changes (calories) 1. What is the number of calories needed to increase the temperature of 50.0 g of water from 30.0 to 45.0 deg C? 2. What temperature change in Celsius degrees is produced when 800 calories are absorbed by 100 g of water? 3. How many grams of water can be heated from 20.0 o C to 95.0 o C by the absorption of 4.50 kilocalories? 4. How many calories are released when 250 g of water cools from 60.0 to 20.0 o C? 5. What is the final temperature after 80.0 calories are absorbed by 10.0 g of water at 25.0 o C? 6. What is the final temperature when 640. calories are given off by 40.0 g of water at 45.0 o C? 4

5 HW #4: Worksheet on Energy Changes (Calorimetry) 1. A 85.0 g sample of Al is heated to 60.3 o C. The Aluminum is then placed in g of water at 20.0 o C. The final temperature of the mixture is 22.5 o C. What is the specific heat of Al? 2. A 15.5 g piece of chromium is heated to deg C and then placed in a calorimeter containing 55.5 g of water at 16.5 deg. C. The final temperature of the water is 18.9 deg. C. What is the specific heat of chromium? 3. A g sample of a metal at 75.0 o C is added to g of H 2 O at 15.0 o C. The temperature of the water rises to 18.3 o C. Calculate the specific heat of the metal. 5

6 1. Given Reaction #1 below, find the H for the reactions #2 and #3. Reaction #1: 2Ag (s) + Br 2 (l) 2AgBr(s) H = -199kJ Reactions #2: AgBr(s) Ag (s) +1/2 Br 2 (l) H =?????? Reaction #3 : 2AgBr(s) 2Ag (s) + Br 2 (l) H =?????? 2. Given the reaction: 2H 2 (l) + O 2 (l) 2H 2 O(l) H = kJ Calculate H for the equation: H 2 O(l) H 2 (l) + 1/2O 2 (l) 3. Consider the following thermochemical equation: H 2 (g) + Cl 2 (g) 2HCl(g) H= -185kJ Calculate H when a. one mole of HCl is formed b. 1.0 g of Cl 2 reacts c. 2.5g of HCl reacts CONTINUE TO THE NEXT PAGE 6

7 4. Calcium carbide, CaC 2, is the raw material for the production of acetylene. Calcium carbide is produced by the reacting calcium oxide with carbon, producing carbon monoxide as a by-product. When one mole of CaC 2 is formed, 464.8kJ is absorbed. a. write a thermochemical equation for this reaction. b. Is the reaction exothermic or endothermic? c. What is H when 1.00 g of CaC 2 (g) is formed? 7

8 Hess's Law Worksheet #6 Directions: Solve the following problems using Hess s Law. 1. Calculate H for the reaction: C 2 H 4 (g) + H 2 (g) C 2 H 6 (g), from the following data. C 2 H 4 (g) + 3 O 2 (g) 2 CO 2 (g) + 2 H 2 O (l) C 2 H 6 (g) + 3½ O 2 (g) 2 CO 2 (g) + 3 H 2 O (l) H 2 (g) + ½ O 2 (g) H 2 O (l) H = kj H = kj H = kj 2. Calculate H for the reaction 4 NH 3 (g) + 5 O 2 (g) 4 NO (g) + 6 H 2 O (g), from the following data. N 2 (g) + O 2 (g) 2 NO (g) N 2 (g) + 3 H 2 (g) 2 NH 3 (g) H = kj H = kj 2 H 2 (g) + O 2 (g) 2 H 2 O (g) H = kj 3. Find H for the reaction 2H 2 (g) + 2C(s) + O 2 (g) C 2 H 5 OH(l), using the following. C 2 H 5 OH (l) + 2 O 2 (g) 2 CO 2 (g) + 2 H 2 O (l) C (s) + O 2 (g) CO 2 (g) H 2 (g) + ½ O 2 (g) H 2 O (l) H = kj H = kj H = kj CONTINUE TO THE NEXT PAGE 8

9 4. Calculate H for the reaction CH 4 (g) + NH 3 (g) HCN (g) + 3 H 2 (g), given: N 2 (g) + 3 H 2 (g) 2 NH 3 (g) C (s) + 2 H 2 (g) CH 4 (g) H 2 (g) + 2 C (s) + N 2 (g) 2 HCN (g) H = kj H = kj H = kj 5. Calculate for the reaction 2 Al (s) + 3 Cl 2 (g) 2 AlCl 3 (s) from the data. 2 Al (s) + 6 HCl (aq) 2 AlCl 3 (aq) + 3 H 2 (g) H = kj HCl (g) HCl (aq) H 2 (g) + Cl 2 (g) 2 HCl (g) AlCl 3 (s) AlCl 3 (aq) H = kj H = kj H = kj 9

10 Standard Heats of Formation (Worksheet #7) Use a standard enthalpies of formation table to determine the change in enthalpy ( H) for each of these reactions. 1. a) 2 CO(g) + O 2 (g) 2 CO 2 (g) b) CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(l) c) 2 H 2 S(g) + 3 O 2 (g) 2 H 2 O(l) + 2 SO 2 (g) 2. a) CaCO 3 (s) CaO(s) + CO 2 (g) b) CH 4 (g) + 2Cl 2 (g) CCl 4 (l) + 2H 2 (g) c) N 2 (g) + 2O 2 (g) 2NO 2 (g) 10

11 Entropy and Free Energy Worksheet #8 1. Compare the conditions or formula for each of the following and circle the one with the higher entropy. Next, briefly state WHY you chose the one you did. A. O 2 (g) at 0 deg. C OR O 2 (g) at -50 deg. C Why? B. I 2 (s) at room temp. OR I 2 (g) at room temp. Why? 2. Compare the products with the reactants and circle whether S for the reaction will be negative or positive. (NO calculations!) Next, briefly state WHY you chose the one you did. A. Is S negative OR positive for: I 2 (g) 2 I (g) Why? B. Is S negative OR positive for: P 4 (s) + 6 H 2 (g) 4PH 3 (g) Why? C. Is S negative OR positive for: 2SO 2 (g) + O 2 (g) 2SO 3 (g) Why? CONTINUE TO THE NEXT PAGE 11

12 3. Using the summation equation and your reference booklet, calculate S for the following reaction: 2 Na (s) + 2 H 2 O( l) 2 NaOH (aq) + H 2 (g) 4. Given the values of H, S, and T below, a. calculate G for each of the following, using the Gibbs Equation ( G = H -T S). b. State whether the reaction is spontaneous, based on the sign of G. A. Ca (s) + 2H 2 O (l) Ca(OH) 2 (aq) + H 2 (g) H = kj/mol S = J/mol K T = 25 deg. C B. 6 C (s) + 3H 2 (g) C 6 H 6 (l) H = 49.0 kj/mol S = J/mol K T = 25 deg. C 12