On this occasion chemistry classes brings you the concept of thermochemical ecauciones:

Thermochemical equations simultaneously express the relations of mass and energy (more commonly enthalpy). (Remember that the ENTHALPY is designated with the letter H and is the heat liberated/ABSORBED at constant pressure)

__Guide to write and interpret thermochemical equations__.

2. – When you write thermochemical equations must be specified all the reagents and products physical States, because they depend on the actual changes of enthalpy (H). Using the following notation: (s) solid, (l) (g) and liquid gas.

#### The enthalpy of the reaction of formation of water depends on the physical state (gas, liquid, solid)

3. – The amount of heat associated with the reaction always is written on the right side, the reaction will be exothermic if the DeltaH has negative value, and endothermic if the DeltaH has positive value.

4. – When reverses an equation, change the roles of the reagents and products. Consequently, the magnitude of DeltaH to the equation is the same but changes sign

5. – If both sides of the equation are multiplied by the factor n, then also changes by the same factor.