Worksheet: Enthalpy Measurements

In this worksheet, we will practice using calorimetry data to determine enthalpy changes during phase changes and chemical reactions.

Q1:

What is the standard enthalpy change for the following reaction? BH()+6HO()2B(OH)()+6H()26232glsg

SubstanceBH()26gHO()2lB(OH)()3sH()2g
Δ𝐻⦡f(kJ/mol)36.4βˆ’285.83βˆ’1,094.330

Q2:

What is the standard enthalpy change for the following reaction? Give your answer to 1 decimal place. BCl()+3HO()B(OH)()+3HCl()323glsg

SubstanceBCl()3gHO()2lB(OH)()3sHCl()g
Δ𝐻(/)⦡fkJmolβˆ’403.8βˆ’285.83βˆ’1,094.33βˆ’92.307

Q3:

What is the standard enthalpy change for the following reaction? BF()+3HO()B(OH)()+3HF()323glsg

SubstanceBF()3gHO()2lB(OH)()3sHF()g
Δ𝐻⦡f(kJ/mol)βˆ’1,136.0βˆ’285.83βˆ’1,094.33βˆ’273.3

Q4:

When solid ammonium nitrate dissolves in water, the solution becomes cold. This is the basis for an β€œinstant ice pack”:

When 3.21 g of solid NHNO43 dissolves in 50.0 g of water at 24.9∘C in a calorimeter, the temperature decreases to 20.3∘C. Assuming that the water has a specific heat capacity of 4.184/β‹…JgC∘:

Calculate the value of q for this reaction

  • Aβˆ’1,000 J
  • B+1,000 J
  • Cβˆ’960 J
  • D+960 J
  • E+1,000 J

What is the molar enthalpy for the dissolution of ammonium nitrate in water?

  • A52 kJ/mol
  • B22 kJ/mol
  • C19 kJ/mol
  • D26 kJ/mol
  • E35 kJ/mol

Q5:

Dissolving 3.0 g of CaCl()2s in 150.0 g of water in a calorimeter at 22.4∘C causes the temperature to rise to 25.8∘C.

What is the approximate amount of heat involved in the dissolution, assuming the heat capacity of the resulting solution is 4.184/β‹…JgC∘?

Q6:

Calculate, to 2 decimal places, the enthalpy change produced from the thermal decomposition of 126 g of magnesium carbonate, its molar mass is 84.313 g/mol, under constant pressure according to the given equation. MgCOMgO+COkJmol32Δ𝐻=+118/

  • Aβˆ’176.34 kJ
  • B+78.96 kJ
  • C+176.34 kJ
  • Dβˆ’78.96 kJ

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