Question

Pentane is a liquid and its formula is C3H₁2(1). When pentane reacts with

oxygen gas, it produces water and carbon dioxide gas. The enthalpy of this reaction is
-3,510 kJ. Write a correct thermochemical equation for this reaction, explain how you
came up with this equation, and explain what it tells you about the reaction. Make sure to
balance the chemical equation, include states of matter for each substance, and explain
why the enthalpy of the reaction is negative to earn full credit.

Answer 1

The balanced thermochemical equation for the reaction of pentane (C5H12) with oxygen gas (O2) to produce water (H2O) and carbon dioxide (CO2) is:

C5H12 (l) + 8 O2 (g) → 5 CO2 (g) + 6 H2O (l) ΔH = -3,510 kJ

The equation is balanced by making sure there are equal numbers of atoms of each element on both the reactant and product sides of the equation. The states of matter are included in the equation to show the physical state of each substance, with (l) indicating a liquid and (g) indicating a gas.

The negative value of enthalpy (ΔH) indicates that this reaction is exothermic, meaning that it releases heat to the surroundings. In other words, the products of the reaction have a lower enthalpy than the reactants. This can be explained by the fact that the bonds formed between carbon and oxygen in CO2 and between hydrogen and oxygen in H2O are stronger than the bonds broken between carbon and hydrogen in C5H12 and between oxygen atoms in O2. The excess energy is released in the form of heat, resulting in a negative value for ΔH.