3.3 - Energy Value as a Term in a Balanced Equation
Completion requirements
Module 3
Lesson 3.3 Energy Value as a Term in Equation
Key Concepts
Enthalpy change can be communicated by including it as a term in a balanced equation.
If the enthalpy change is negative, as in the example below, the reaction is exothermic.
\( \mathrm { C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g) } \)
\( \mathrm { \Delta_rH = -2043.9~kJ } \)
Because energy is produced in an exothermic reaction, we can include it as a product in the balanced reaction.
\( \mathrm { C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g) + 2043.9~kJ } \)
What if the enthalpy change is positive, as in the example below?
\( \mathrm { \frac{1}{2}N_2(g) + \frac{1}{2}O_2(g) \rightarrow NO(g) } \)
\( \mathrm { \Delta_rH = +91.3~kJ } \)
Because energy is absorbed (used up) in an endothermic reaction, it is included as a reactant in the balanced reaction.
\( \mathrm { \frac{1}{2}N_2(g) + \frac{1}{2}O_2(g) + 91.3~kJ \rightarrow NO(g) } \)
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