Dr. Mihelcic

Chemistry 1

2012-13

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 16.00 joules?

2. How many kilojoules are in 25.00 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?

1. A 15.75-g piece of iron absorbs 1086.75 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 1500.0 g of the wood absorbs 6.75×104 joules of heat, and its temperature changes from 32°C to 57°C.

4. 100.0 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 0.129 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!

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 20.0oC to 95.0oC by the absorption of 4.50 kilocalories?

4. How many calories are released when 250 g of water cools from 60.0 to 20.0oC?

5. What is the final temperature after 80.0 calories are absorbed by 10.0 g of water at 25.0oC?

6. What is the final temperature when 640. calories are given off by 40.0 g of water at 45.0oC?

1. A 85.0 g sample of Al is heated to 60.3oC. The Aluminum is then placed in 150.0 g of water at 20.0oC. The final temperature of the mixture is 22.5oC. What is the specific heat of Al?

2. A 15.5 g piece of chromium is heated to 100.0 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 150.0 g sample of a metal at 75.0oC is added to 150.0 g of H2O at 15.0oC. The temperature of the water rises to 18.3oC. Calculate the specific heat of the metal.

1. Given Reaction #1 below, find the ∆H for the reactions #2 and #3.

Reaction #1: 2Ag (s) + Br2 (l) à 2AgBr(s) ∆H = -199kJ

Reactions #2: AgBr(s) à Ag (s) +1/2 Br2(l) ∆H = ??????

Reaction #3 : 2AgBr(s) à 2Ag (s) + Br2 (l) ∆H = ??????

2. Given the reaction: 2H2(l) + O2(l) à 2H2O(l) ∆H = -571.6kJ

Calculate ∆H for the equation: H2O(l) à H2(l) + 1/2O2(l)

3. Consider the following thermochemical equation: H2(g) + Cl2(g) à 2HCl(g) ∆H= -185kJ

Calculate ∆H when

a. one mole of HCl is formed

b. 1.0 g of Cl2 reacts

c. 2.5g of HCl reacts

CONTINUE TO THE NEXT PAGE →

4. Calcium carbide, CaC2, 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 CaC2 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 CaC2(g) is formed?

Hess's Law Worksheet #6

Directions: Solve the following problems using Hess’s Law.

  1. Calculate DH for the reaction: C2H4 (g) + H2 (g) ® C2H6 (g), from the following data.

C2H4 (g) + 3 O2 (g) ® 2 CO2 (g) + 2 H2O (l) / DH = -1411. kJ
C2H6 (g) + 3½ O2 (g) ® 2 CO2 (g) + 3 H2O (l) / DH = -1560. kJ
H2 (g) + ½ O2 (g) ® H2O (l) / DH = -285.8 kJ
  1. Calculate DH for the reaction 4 NH3 (g) + 5 O2 (g) ® 4 NO (g) + 6 H2O (g), from the following data.

N2 (g) + O2 (g) ® 2 NO (g) / DH = -180.5 kJ
N2 (g) + 3 H2 (g) ® 2 NH3 (g) / DH = -91.8 kJ
2 H2 (g) + O2 (g) ® 2 H2O (g) / DH = -483.6 kJ
  1. Find DH° for the reaction 2H2(g) + 2C(s) + O2(g) ® C2H5OH(l), using the following.

C2H5OH (l) + 2 O2 (g) ® 2 CO2 (g) + 2 H2O (l) / DH = -875. kJ
C (s) + O2 (g) ® CO2 (g) / DH = -394.51 kJ
H2 (g) + ½ O2 (g) ® H2O (l) / DH = -285.8 kJ

CONTINUE TO THE NEXT PAGE →

  1. Calculate DH for the reaction CH4 (g) + NH3 (g) ® HCN (g) + 3 H2 (g), given:

N2 (g) + 3 H2 (g) ® 2 NH3 (g) / DH = -91.8 kJ
C (s) + 2 H2 (g) ® CH4 (g) / DH = -74.9 kJ
H2 (g) + 2 C (s) + N2 (g) ® 2 HCN (g) / DH = +270.3 kJ

5.  Calculate DH for the reaction 2 Al (s) + 3 Cl2 (g) ® 2 AlCl3 (s) from the data.

2 Al (s) + 6 HCl (aq) ® 2 AlCl3 (aq) + 3 H2 (g) / DH = -1049. kJ
HCl (g) ® HCl (aq) / DH = -74.8 kJ
H2 (g) + Cl2 (g) ® 2 HCl (g) / DH = -1845. kJ
AlCl3 (s) ® AlCl3 (aq) / DH = -323. kJ
Use a standard enthalpies of formation table to determine the change in enthalpy (∆H) for each of these reactions.
1. / a) 2 CO(g) + O2(g) à 2 CO2(g)
b) CH4(g) + 2 O2(g) à CO2(g) + 2 H2O(l)
c) 2 H2S(g) + 3 O2(g) à 2 H2O(l) + 2 SO2(g)

2. a) CaCO3(s) à CaO(s) + CO2(g)

b) CH4(g) + 2Cl2(g) à CCl4(l) + 2H2(g)

c) N2(g) + 2O2(g) à2NO2(g)

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. O2 (g) at 0 deg. C OR O2 (g) at -50 deg. C

Why? ______

B. I2 (s) at room temp. OR I2 (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:

I2 (g) à 2 I (g)

Why? ______

B. Is ∆S negative OR positive for:

P4 (s) + 6 H2 (g) à 4PH3 (g)

Why? ______

C. Is ∆S negative OR positive for:

2SO2 (g) + O2 (g) à 2SO3 (g)

Why? ______

CONTINUE TO THE NEXT PAGE →

3. Using the summation equation and your reference booklet, calculate ∆S for the following reaction:

2 Na (s) + 2 H2O( l) à 2 NaOH (aq) + H2 (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) + 2H2O (l) à Ca(OH)2 (aq) + H2 (g)

∆H = - 431.2 kJ/mol ∆S = - 125 J/mol K T = 25 deg. C

B. 6 C (s) + 3H2 (g) à C6H6 (l)

∆H = 49.0 kJ/mol ∆S = - 253.5 J/mol K T = 25 deg. C

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Dr. Mihelcic

Honors Chemistry 2012-13