MRE_Yr 12 Hess Law

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

Hess' Law makes use of which principle to calculate the enthalpy change of a reaction?

• The law of conservation of energy

• The law of conservation of matter

• The law that you will always find a lost item in the last place you look for it

• Murphy's law

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.

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.

In order to find the enthalpy of combustion of C₃H₈ how must the enthalpy changes be arranged?

• ΔH₃ = ΔH₁ + ΔH₂

• ΔH₂ = ΔH₃ - ΔH₁

• ΔH₁ = ΔH₂ - ΔH₃

• 0 = ΔH₁ + ΔH₂ + ΔH₃

Standard conditions are defined as...

• 298K and 1.00 x 10⁵ kPa

• 273K and 1.00 x 10⁵ kPa

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