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 9 9 . 0 C to 3 5 . 0 C , as the heat provided when 95.0 g of steam is cooled from 1 1 0 C to 1 0 0 C ? Use 4 . 1 8 4 / J g C for the specific heat capacity of water and 2 . 0 9 3 / J g C for the specific heat capacity of steam.

Q2:

Joseph Priestley prepared oxygen in 1 7 7 4 by heating red mercury(II) oxide with sunlight focused through a lens. How much heat is required to decompose exactly 2 mol of red H g O ( ) 𝑠 to H g ( ) 𝑙 and O ( ) 2 𝑔 under standard conditions? The standard enthalpy of formation of H g O ( ) 𝑠 is 9 0 kJ/mol.

Q3:

The enthalpy of combustion of hard coal averages 3 5 kJ/g, and that of gasoline is 1 . 2 8 × 1 0 5 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 1 3 9 . 7 kJ/mol.

Q5:

The enzyme catalase catalyzes the decomposition of hydrogen peroxide by the exothermic reaction

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 2 5 C . 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 H O ( ) 2 2 a q and H O ( ) 2 l are: Δ 𝐻 = 1 9 1 . 1 7 / f k J m o l and Δ 𝐻 = 2 8 5 . 8 3 / f k J m o l respectively. The heat capacity of the solution may be taken as 4.18 kJ/K⋅L.

Q6:

For water at 3 7 . 0 C , the enthalpy of vaporization is 43.46 kJ/mol. How much heat is required to evaporate 1.50 L of water at 3 7 . 0 C ?

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

Q7:

Propane C H 3 8 is a hydrocarbon that is commonly used as a fuel. The heat of combustion of propane is 2 2 1 9 . 2 kJ/mol.

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

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

What volume of air at 2 5 C and 1.00 atmosphere is needed to completely combust 25.0 grams of propane? Assume that air is 21.0% O 2 by volume and all components of air are ideal gases.

What is the heat of formation, Δ 𝐻 f , of propane given that Δ 𝐻 f of H O ( ) 2 l = 2 8 5 . 8 kJ/mol and Δ 𝐻 f of C O ( ) 2 g = 3 9 3 . 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.

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