Question

1. Which of the following is a correctly written thermochemical equation?

NH4Cl NH4+ + Cl
2C8H18 + 25O2 16CO2 + 18H2O, H = 5,471 kJ/mol
Fe (s) + O2 (g) Fe2O3 (s), H = 3,926 kJ
-->C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (l), H = 2,220 kJ/mol
2. How does a phase change affect a thermochemical equation?

It alters the moles of reactants.
-->It can affect the (delta) H value.
It alters the products.
It affects the balance of the equation.

Answer 1

1. Which of the following is a correctly written thermochemical equation?C3H8 (g) + 5O2 (g) 3CO2 (g) + 4H2O (l), H = 2,220 kJ/mol

It is the answer because it shows everything needed to describe a reaction. It has the state and the heat of reaction.

2. How does a phase change affect a thermochemical equation?

It can affect the (delta) H value. It can either increase or decrease that value.

Answer 2

Explanation:

1. Thermochemical equation is balance stoichiometric chemical equation written with the phases of the reactants and products in the brackets along with the enthalpy change of the reaction.

The given correct thermochemical reactions are:

$Fe(s)+O_2(g)\rightarrow Fe_2O_3(s),\Delta H = 3,926 kJ$

$C_3H_8(g)+5O_2 (g)\rightarrow 3CO_2 (g)+4H_2O(l),\Delta H= 2,220 kJ/mol$

2. Phase change affect the value of the enthalpy change of the thermochemical equation. This is because change in phase is accompanied by change in energy. For example:

$H_2O(s)\rightarrow H_2O(g),\Delta H_{s}=51.1 kJ/mol$

$H_2O(l)\rightarrow H_2O(g),\Delta H_{v}=40.65 kJ/mol$

In both reaction phase of water is changing with change in energy of enthalpy of reaction.