Practice Hess's Law

Calculate the enthalpy for the oxidation of CO to CO₂ using the enthalpy of reaction for the combustion of C to CO (ΔH = -221.0 kJ) and the enthalpy for the combustion of C to CO₂ (ΔH = -393.5 kJ).

2CO(g) + O₂(g)  →  2CO₂(g)  ΔH = ?

C(s) + O₂(g)  →  CO₂(g)  ΔH = -393.5 kJ

2C(s) + O₂(g)  →  2CO(g)  ΔH = -221.0 kJ

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Calculate the enthalpy for the combustion reaction of sulfur to sulfur trioxide using the enthalpies of the two reactions shown below:

2S(s) + 3O₂(g)  →  2SO₃(g)  ΔH = ?

S(s) + O₂(g)  →  SO₂(g)  ΔH = -297 kJ

2SO₃(g)  → 2SO₂(g) + O₂(g)  ΔH = 198 kJ

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Using the Hess’s law, calculate ΔH^o for the combustion reaction of butene:

C₄H₈(g) + 6O₂(g) → 4CO₂(g) + 4H₂O(l), ΔH^o = ?

Use the following reactions and given ΔH’s:

1) 2H₂(g) + O₂(g) → 2H₂O(g), ΔH^o = -571 kJ

2) C₄H₈(g) + H₂(g) → C₄H₁₀(g), ΔH^o = -126 kJ

3) 2C₄H₁₀(g) + 13O₂(g) → 8CO₂(g) + 10H₂O(l), ΔH^o = -5754 kJ

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Using the Hess’s law and the enthalpies of the three combustion reactions below, calculate the enthalpy of the reaction producing methanol (CH₃OH) from carbon monoxide and hydrogen gas.

CO(g) + 2H₂(g) → CH₃OH(g), ΔH = ?

1) 2CO(g) + O₂(g) → 2CO₂(g), ΔH = -566 kJ

2) 2H₂(g) + O₂(g) → 2H₂O(g), ΔH^o = -571 kJ

3) 2CH₃OH(g) + 3O₂(g) → 2CO₂(g) + 4H₂O(g), ΔH^o = −1430 kJ

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Using the Hess’s law and the enthalpies of the given reactions, calculate the enthalpy of the combustion reaction of CH₃Cl:

CH₃Cl(g) + O₂(g) → CO(g) + HCl(g) + H₂O(l), ΔH = ?

1) CO(g) + 2H₂(g) → CH₃OH(g), ΔH^o = -139 kJ

2) 2H₂(g) + O₂(g) → 2H₂O(g), ΔH^o = -571 kJ

3) CH₃OH(g) + HCl(aq) → CH₃Cl(g) + H₂O(l), ΔH^o = -28 kJ

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NGSS.HS-PS1-4

Using the Hess’s law and the enthalpies of the given reactions, calculate the enthalpy of the following oxidation reaction of ammonia:

4NH₃(g) + 5O₂(g) → 4NO(g) + 6H₂O(g), ΔH = ?

1) N₂(g) + 3H₂(g) → 2NH₃(g), ΔH = -92 kJ

2) 2H₂(g) + O₂(g) → 2H₂O(g), ΔH = -484 kJ

3) N₂(g) + O₂(g) → 2NO(g), ΔH = 181 kJ

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NGSS.HS-PS1-4

Using the Hess’s law and the enthalpies of the given reactions, calculate the enthalpy of the following oxidation reaction between CuO and HCl:

2CuO(s) + 4HCl(g) → 2CuCl(s) + Cl₂(g) + 2H₂O(g), ΔH = ?

1) CuO(s) + H₂(g) → Cu(s) + H₂O(g), ΔH = -85 kJ

2) 2Cu(s) + Cl₂(g) → 2CuCl(s), ΔH = -274 kJ

3) H₂(g) + Cl₂(g) → 2HCl(g), ΔH = -184 kJ

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Determine the enthalpy of formation of methane using the following data obtained from bomb calorimetry:

 

C(graphite) + 2H₂(g) → CH₄(g) ΔH °_f = ?

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CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH ° = -891 kJ

C(s) + O₂(g) → CO₂(g) ΔH = -393 kJ

2H₂(g) + O₂(g) → 2H₂O(l) ΔH = -572 kJ

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Calculate the ΔH_f for the following reaction:

   2NaHCO₃ (s)  → Na₂CO₃ (s) + CO₂ (g) + H₂O (I)

The table shows the standard enthalpy of formations (ΔH_f) relevant to this reaction.

Answer explanation

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NGSS.HS-PS1-4

NGSS.HS-PS3-1

Calculate ΔH_f [ethane].

The relevant change in standard enthalpy of combustion (ΔH_c) values are shown in the table:

Answer explanation

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NGSS.HS-PS3-1