Quiz on Thermochemistry

The following reaction is an exothermic reaction: CH4(g)+2O2(g)→CO2(g)+2H2O(g). If it is known that the enthalpy change (ΔH) of the reaction is −890kJ/mol, which of the following statements is true?

• The system absorbs 890 kJ of energy.

• This reaction occurs with the release of 890 kJ of energy.

• The system requires 890 kJ of energy to proceed.

• This reaction is endothermic because it produces water.

• This reaction does not experience a change in enthalpy.

Given the reaction equation: 2H2(g)+O2(g) →2H2O(g). If the enthalpy change (ΔH) for this reaction is −483.6 kJ, what is the ΔH for the formation of 1 mol of steam?

• −483.6 kJ

• −241.8 kJ

• −121.9 kJ

• −60.95 kJ

• −30.47 kJ

For the following reaction: N2(g)+3H2(g) →2NH3(g). If the standard enthalpy of formation ΔHf∘ for NH3(g) is −46.1kJ/mol, what is the enthalpy change of the above reaction (ΔH)?

• −92.2 kJ

• −46.1 kJ

• +46.1 kJ

• +92.2 kJ

• 0 kJ

If an endothermic reaction occurs, which of the following statements is true?

• The system releases heat to the environment.

• The temperature of the system will increase during the reaction.

• Heat is absorbed from the environment into the system.

• ΔH is negative.

• The reaction does not involve energy.

Which statement is true regarding the standard enthalpy change of formation (ΔHf∘) of a substance?

• Its value is always positive for all substances.

• For elements in standard state, ΔHf is zero.

• ΔHf∘ only applies to organic compounds.

• The value of ΔHf∘ is always measured at 100°C.

• The more stable a substance, the larger the positive value of ΔHf.

Given the reaction equation: 2NO(g) + O2(g) → 2NO2(g). If the enthalpy change (ΔH) for the above reaction is −114kJ, what happens to the system?

• Heat is absorbed from the environment by the system.

• This reaction does not require energy to proceed.

• Heat is released from the system.

The reaction above has a change of -114 kJ, what happens to the system?

• Heat is absorbed from the environment by the system.

• This reaction does not require energy to occur.

• Heat is released from the system to the environment.

• The reaction occurs endothermically.

• The reaction produces more energy than it consumes.

If 50 kJ of heat is released during the combustion of butane (C4H10) in the air, this reaction is classified as...

• Endothermic because energy is absorbed.

• Exothermic because energy is released.

• Exothermic because the system absorbs energy.

• Endothermic because energy is released.

• There is no change in energy in this reaction.

The formation reaction of ammonia from nitrogen gas and hydrogen gas is: N2(g)+3H2(g)→2NH3(g) If the enthalpy change (ΔH) of the reaction is -92.4 kJ/mol, which statement about this reaction is correct?

• This reaction is endothermic and ΔH is positive.

• This reaction is exothermic and ΔH is negative.

• This reaction is exothermic and ΔH is positive.

• This reaction is endothermic and ΔH is negative.

• This reaction does not involve a change in heat.

The correct statement regarding enthalpy is...

• Enthalpy is only measured for chemical reactions at high temperatures.

• Enthalpy is the amount of energy required to convert a substance into gas.

• Enthalpy is the energy possessed by the system at constant pressure.

• Enthalpy is only used for combustion reactions.

• Enthalpy is not affected by environmental conditions.