Thermochemistry and Energy Flashcards

Using Hess's Law, if Reaction A has ΔH = +100 kJ and Reaction B has ΔH = –150 kJ, what is ΔH for the overall reaction A + B?

Answer: –50 kJ

Adding the two enthalpies: +100 kJ + (–150 kJ) = –50 kJ for the combined overall reaction.

Which of the following has the highest specific heat capacity?

Answer: Water (4.18 J/g·°C)

Water has a specific heat of 4.18 J/(g·°C), far higher than common metals, making it an excellent thermal reservoir.

The standard enthalpy of combustion is defined as the enthalpy change when one mole of a substance burns completely in:

Answer: Excess oxygen

Standard enthalpy of combustion is measured when one mole of substance burns completely in excess oxygen under standard conditions.

A hand warmer packet releases heat as iron oxidizes. This is an example of a(n):

Answer: Exothermic chemical reaction

Iron oxidation releases energy as heat, making hand warmers a real-world example of an exothermic chemical reaction.

What is the term for the minimum energy required to break all bonds in one mole of a gaseous molecule?

Answer: Bond dissociation energy

Bond dissociation energy is the energy required to homolytically break a specific bond in one mole of gaseous molecules.

For the reaction: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l), ΔH = –890 kJ. This value indicates the reaction:

Answer: Releases 890 kJ per mole of CH₄ burned

A ΔH of –890 kJ means 890 kJ of heat is released to the surroundings for every mole of methane combusted.