CHEM 1060 Lecture Notes - Lecture 2: Chemical Equation, Joule, Complement Factor B

1- The molar heat capacity of silver is 25.35 J/mol⋠∘C. How much energy would it take to raise the temperature of 8.20 g of silver by 14.5 ∘C?

Express your answer with the appropriate units.

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Part A

Calculate the enthalpy of the reaction

2NO(g)+O2(g)→2NO2(g)

given the following reactions and enthalpies of formation:

12N2(g)+O2(g)→NO2(g), ΔH∘A=33.2 kJ

12N2(g)+12O2(g)→NO(g), ΔH∘B=90.2 kJ

Express your answer with the appropriate units.

2- A total of 2.00 mol of a compound is allowed to react with water in a foam coffee cup and the reaction produces 196 g of solution. The reaction caused the temperature of the solution to rise from 21.00 to 24.70 ∘C. What is the enthalpy of this reaction? Assume that no heat is lost to the surroundings or to the coffee cup itself and that the specific heat of the solution is the same as that of pure water.

Enter your answer in kilojoules per mole of compound to three significant figures.

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3- A volume of 110. mL of H2O is initially at room temperature (22.00 ∘C). A chilled steel rod at 2.00 ∘Cis placed in the water. If the final temperature of the system is 21.00 ∘C , what is the mass of the steel bar?

Use the following values:

specific heat of water = 4.18 J/(g⋠∘C)

specific heat of steel = 0.452 J/(g⋠∘C)

Express your answer to three significant figures and include the appropriate units.

Part B

The specific heat of water is 4.18 J/(g⋠∘C). Calculate the molar heat capacity of water.

Express your answer to three significant figures and include the appropriate units.

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4- What is the enthalpy for the following reaction?

overall: N2O4→2NO2

Express your answer numerically in kilojoules per mole.

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Part B

Calculate the enthalpy of the reaction

4B(s)+3O2(g)→2B2O3(s)

given the following pertinent information:

B2O3(s)+3H2O(g)→3O2(g)+B2H6(g), ΔH∘A=+2035 kJ

2B(s)+3H2(g)→B2H6(g), ΔH∘B=+36 kJ

H2(g)+12O2(g)→H2O(l), ΔH∘C=−285 kJ

H2O(l)→H2O(g), ΔH∘D=+44 kJ

Express your answer with the appropriate units.

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5- What is the balanced chemical equation for the reaction used to calculate ΔH∘f of MgCO3(s)?

If fractional coefficients are required, enter them as a fraction (i.e. 1/3). Indicate the physical states using the abbreviation (s), (l), or (g) for solid, liquid, or gas, respectively without indicating allotropes. Use (aq) for aqueous solution.

Express your answer as a chemical equation.

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6- Part A

Determine the enthalpy for this reaction:

Ca(OH)2(s)+CO2(g)→CaCO3(s)+H2O(l)

Express your answer in kilojoules per mole to one decimal place.

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Part B

Consider the reaction

Ca(OH)2(s)→CaO(s)+H2O(l)

with enthalpy of reaction

ΔHrxn∘=65.2kJ/mol

What is the enthalpy of formation of CaO(s)?

Express your answer in kilojoules per mole to one decimal place.

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7- Part A

Write a balanced chemical equation depicting the formation of one mole of H2O2(g) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

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Part B

For H2O2(g), find the value of ΔH∘f. (Use Appendix C)

Express your answer using five significant figures.

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PART C: Write a balanced chemical equation depicting the formation of one mole of CaCO3(s) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

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Part D

For CaCO3(s), find the value of ΔH∘f. (Use Appendix C)

Express your answer using five significant figures.

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Part E

Write a balanced chemical equation depicting the formation of one mole of POCl3(l) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

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Part F

For POCl3(l), find the value of ΔH∘f. (Use Appendix C)

Express your answer using four significant figures.

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Part G

Write a balanced chemical equation depicting the formation of one mole of C2H5OH(l) from its elements in their standard states.

Express your answer as a chemical equation. Identify all of the phases in your answer.

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Part H

For C2H5OH(l), find the value of ΔH∘f. (Use Appendix C)

Express your answer using four significant figures.

Show your work for all calculations.

1. When 1.104 grams of iron metal are mixed with 26.023 grams of hydrochloric acid in a coffee cup calorimeter, the temperature rises from 25.2 °C to a maximum of 33.5 °C. The reaction that occurs is given below.

2Fe(s)+6HCl(aq) → 2FeCl3 (aq)+3H2 (g)

a) Determine the amount of heat (in J) absorbed by the reaction mixture. Assume that the specific heat capacity of the mixture is the same as the specific heat capacity of water.

b) How much heat (in J) was released by the reaction that occurred?

c) Is this reaction exothermic or endothermic? Is ΔHreaction positive or negative?

d) Under constant pressure conditions (as used in this experiment), the heat released by the reaction equals the reaction enthalpy, qreleased = ΔHreaction. Determine ΔHreaction in Joules per gram of metal used (J/g).

e) Determine ΔHreaction in kilojoules per mole of metal used (kJ/mol).

f) Determine ΔHreaction in kilojoules per mole for the balanced reaction equation provided (kJ/mol). 

2. Consider the following three reactions:

2Fe(s)+6HCl(aq) → 2FeCl3 (aq)+3H2 (g) ΔHA

Fe2O3 (s)+6HCl(aq) → 2FeCl3 (aq)+3H2O(l) ΔHB

2H2 (g) + O2 (g) → 2H2O(l) ΔHC

Show how these equations must be summed together according to Hess’s Law to determine ΔH for the combustion of iron (target equation shown below). Also show clearly how the ΔH values of each of the three reactions must be manipulated to determine the enthalpy of combustion of iron.

4Fe(s)+3O2 (g) → 2Fe2O3 (s) ΔH=?

3. Using tabulated ΔHf° values in the text, determine the enthalpy change (in kJ/mol) that occurs during the formation of water from its elements as described by the equation:

2H2 (g) + O2 (g) → 2H2O(l) ΔH=?