Worksheet: Converting Enthalpy to Heat

In this worksheet, we will practice calculating an enthalpy change from tabulated enthalpies and converting this value to a temperature change.

Q1:

Homes may be heated by pumping hot water through radiators. What mass of water will provide the same amount of heat when cooled from 99.0C to 35.0C, as the heat provided when 95.0 g of steam is cooled from 110C to 100C? Use 4.184/JgC for the specific heat capacity of water and 2.093/JgC for the specific heat capacity of steam.

Q2:

Joseph Priestley prepared oxygen in 1,774 by heating red mercury(II) oxide with sunlight focused through a lens. How much heat is required to decompose exactly 2 mol of red HgO()𝑠 to Hg()𝑙 and O()2𝑔 under standard conditions? The standard enthalpy of formation of HgO()𝑠 is 90 kJ/mol.

Q3:

The enthalpy of combustion of hard coal averages 35 kJ/g, and that of gasoline is 1.28×10 kJ/gal. How many kilograms of hard coal provide the same amount of heat as is available from 1.0 gallon of gasoline?

Q4:

How much heat is produced when 1.50 g of chromium metal reacts completely with oxygen gas under standard conditions? The standard enthalpy of formation of chromium(III) oxide is 1,139.7 kJ/mol.

Q5:

The enzyme catalase catalyzes the decomposition of hydrogen peroxide by the following exothermic reaction HO()HO()O()2222aqlg+12

Suppose that a small amount of solid catalase is added to a 0.1 M aqueous solution of hydrogen peroxide in a calorimeter, with the initial temperature of the solution being 25C. If all the heat liberated in the reaction is retained by the solution, what will be the final temperature of the solution after the reaction mixture has reached its final equilibrium state?

The heats of formation for HO()22aq and HO()2l are Δ𝐻=191.17/fkJmol and Δ𝐻=285.83/fkJmol respectively. The heat capacity of the solution may be taken as 4.18 kJ/K⋅L.

Q6:

For water at 37.0C, the enthalpy of vaporization is 43.46 kJ/mol. How much heat is required to evaporate 1.50 L of water at 37.0C?

  • A 6 . 2 2 × 1 0 kJ
  • B 2 . 4 1 × 1 0 kJ
  • C 6 . 5 2 × 1 0 kJ
  • D 1 . 6 1 × 1 0 kJ
  • E 3 . 6 2 × 1 0 kJ

Q7:

Propane CH38 is a hydrocarbon that is commonly used as a fuel. The heat of combustion of propane is 2,219.2 kJ/mol.

Which of the following is a balanced equation for the complete combustion of propane gas?

  • A C H + 5 O 3 C O + 4 H O 3 8 2 2 2
  • B C H + 4 O 2 C O + 4 H O 3 8 2 2 2
  • C C H + 2 O C O + 2 H O 3 8 2 2 2
  • D 2 C H + 7 O 6 C O + 8 H O 3 8 2 2
  • E C H + 3 O C O + 4 H O 3 8 2 2 2

What volume of air at 25C and 1.00 atmosphere is needed to completely combust 25.0 grams of propane? Assume that air is 21.0% O2 by volume and all components of air are ideal gases.

What is the heat of formation, Δ𝐻f, of propane given that Δ𝐻f of HO()2l = 285.8 kJ/mol and Δ𝐻f of CO()2g = 393.5 kJ/mol?

If all of the heat released by burning 25.0 g of propane is transferred to 4.00 kg of water, how much does the temperature of the water increase? The specific heat capacity of water is 4.184 J/g⋅K.

Q8:

The oxidation of the sugar glucose, CHO6126, is described by the equation: CHO()+6O()6CO()+6HO()kJ6126222sggl,Δ𝐻=2,816.

The metabolism of glucose gives the same products, although glucose in the body is oxidized indirectly by oxygen via a series of reaction steps.

How much heat can be produced by the metabolism of 1.5 g of glucose?

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