Hess's Law and Bond Enthalpies

Based upon the graph above, what type of reaction is this?

• Endothermic

• Exothermic

Tags

NGSS.HS-PS1-4

Consider the following reactions:Fe(s) + 1/2 O2(g) --> FeO(s) H= -272.0 kJ2 Fe(s) + 3/2 O2(g) --> Fe2O3(s) H= -825.5 kJDetermine the delta H for the reaction: 2 FeO(s) + 1/2 O2(g) --> Fe2O3

• -281.5 kJ

• -1097.5 kJ

• -1369.5 kJ

• 281.5 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

The enthalpy change for the reaction, ∆H_r , is equal to 

• ∆H₁ + ∆H₂

• ∆H₁ - ∆H₂

• -∆H₁ - ∆H₂

• -∆H₁ + ∆H₂

Tags

NGSS.HS-PS1-4

Determine the H for reaction of this equation: 3C (graphite) + 4 H2(g) --> C3H8(g)

using these intermediates:

(A) C₃H₈ (g) + 5O₂(g) --> 3CO₂ (g) + 4H₂O (l) H= -2219.9 kJ

(B) C(graphite) + O₂(g) --> CO₂ (g) H= -393.5 kJ

(C) H₂ (g) + 1/2 O₂ (g) --> H₂O (l) H= -285.8 kJ

• -683.4 kJ

• -2899.2 kJ

• -1324.7 kJ

• -104.0 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Using the equations below:

C_(s) + O_2(g) → CO_2(g) ∆H = –390 kJ

Mn_(s) + O_2(g) → MnO_2(s) ∆H = –520 kJ

what is ∆H (in kJ) for the following reaction?

MnO_2(s) + C_(s) → Mn_(s) + CO_2(g)

• 910

• 130

• -130

• -910

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

For Hess' Law to be used what must be the same for all of the reactions being studied?

• The initial conditions of pressure and temperature.

• The final conditions of pressure and temperature.

• The initial and the final conditions of pressure and temperature.

• The initial and the final conditions of pressure and temperature, and the number of moles of reactants.

Consider the following reactions: \( \ce{H2(g) + 1/2 O2(g) -> H2O(l)} \) \( \Delta H = -285.8 \text{ kJ} \) and \( \ce{C(s) + O2(g) -> CO2(g)} \) \( \Delta H = -393.5 \text{ kJ} \). Calculate \( \Delta H \) for the reaction: \( \ce{CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)} \).

• -890.3 kJ

• -802.3 kJ

• -1000.0 kJ

• -750.0 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which of the following statements best describes Hess's Law?

• The total enthalpy change for a reaction is the same, regardless of the number of steps in the reaction.

• The enthalpy change of a reaction depends on the path taken.

• The enthalpy change of a reaction is always positive.

• The enthalpy change of a reaction is always negative.

Given the bond enthalpies: \( \ce{C-H} = 413 \text{ kJ/mol} \), \( \ce{O=O} = 498 \text{ kJ/mol} \), \( \ce{C=O} = 799 \text{ kJ/mol} \), and \( \ce{O-H} = 463 \text{ kJ/mol} \), calculate the \( \Delta H \) for the combustion of methane: \( \ce{CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)} \).

• -802 kJ/mol

• -890 kJ/mol

• -1000 kJ/mol

• -750 kJ/mol

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which of the following is a real-world application of Hess's Law?

• Determining the energy efficiency of a fuel.

• Calculating the speed of a chemical reaction.

• Measuring the pH of a solution.

• Determining the color change in a reaction.