# When 2 moles of potassium chlorate crystals decompose to potassium chloride crystals and oxygen gas at constant temperature and pressure, 44.7 kJ are given off. What is the thermochemical equation?

##### 1 Answer

#### Explanation:

A **thermochemical equation** is simply a chemical equation that contains information about the *enthalpy change of reaction*,

The first thing to do when writing a thermochemical equation is to make sure that you get the balnced chemical equation right.

In your case, you know that **2 moles** of potassium chlorate,

So you know that you have

#2"KClO"_text(3(s]) -> "KCl"_text((s]) + "O"_text(2(g])#

Balance this equation by multiplying the products by

#2"KClO"_text(3(s]) -> 2"KCl"_text((s]) + 3"O"_text(2(g])#

Now focus on the enthalpy change of reaction. The problem tells you that the reaction **given off**

As you know, energy changes are being represent *from the point of view of the system*. This implies that for an exothermic reaction the enthalpy change will carry a **negative sign**, since the system is *losing heat* to the surroundings.

Therefore, the enthalpy change of reaction will be

#DeltaH = -"44. 7 kJ"#

As a result, the *thermochemical equation* for the decomposition of potassium chlorate looks like this

#2"KClO"_text(3(s]) -> 2"KCl"_text((s]) + 3"O"_text(2(g]). " "DeltaH_text(rxn) = -"44.7 kJ"#