2.3 Hess law

What type of reaction is shown in the reaction pathway?

• endothermic reaction
• exothermic reaction

Determine the ΔH_f of CO in the following equation:

C (graphite) + ½O₂ (g) --> CO (g) ΔH_f = ?

Given the following reactions:

C (graphite) + O₂ (g) --> CO₂(g) ΔH₁ = -393.5 kJ mol^-1

CO (g) + ½O₂ (g) --> CO₂ (g) ΔH₂ = -283.0 kJ mol^-1

• -110.5 kJ mol-1

• -676.5 kJ mol-1

• +110.5 kJ mol-1

• +676.5 kJ mol-1

From the data given below

S (s) + O₂ (g) --> SO₂ (g) ΔH₁ = -297 kJ mol^-1

SO₂ (g) + ½O₂ (g) --> SO₃ (g) ΔH₁ = -297 kJ mol^-1

Calculate ΔH for the reaction:

S (s) + ³/₂O₂ (g) --> SO₃ (g)

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

The following equations show the oxidation of carbon and carbon monoxide to carbon dioxide.

C_(s) +O_2(g) → CO_2(g) ΔH = –x kJ mol^–1

CO_(g) + O_2(g) → CO_2(g) ΔH = –y kJ mol^–1

What is the enthalpy change, in kJ mol^–1, for the oxidation of carbon to carbon monoxide?

C_(s) + O_2(g) → CO_(g)

• x + y

• -x - y

• y - x

• x - y

In an endothermic reaction the system is releasing energy.

• True
• False
• Sometimes

A chemical reaction that requires energy is a

• exothermic reaction 
• endothermic reaction 
• over reaction 
• redox reaction

When you freeze water, it turns to ice.  What process is this?

•  Exothermic
• Endothermic
• Condensing
• Melting

Solid magnesium dissolves in a hydrochloric acid, releasing hydrogen gas and heat from a solution of magnesium chloride. What is the sign on ΔH for this reaction?

• Negative because it is exothermic
• Negative because it is endothermic
• Positive because it is exothermic
• Positive because it is endothermic

Which of the following statements are true for the reaction:

SO_2(g) + ¹/₂O_2(g) ↔ SO_3(g) ΔH = –92 kJ mol^-1

Where ↔ indicates that the reaction can proceed in the forward and the reverse direction.

• The forward and reverse reaction both produce 92 kJ of energy.

• Oxidising 2 moles of SO₂ would produce twice as much energy.

• The reverse reaction has an enthalpy of +92 kJ mol^-1.

• Collecting the SO3 produced in the liquid state would not change the measured enthalpy.