Beginner Topic 346 of 1102 Thermodynamics & Energetics
Thermochemical Equation
A balanced equation that includes the enthalpy change for the stated amounts.
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In-depth explanation of Thermochemical Equation
A thermochemical equation is a balanced chemical equation that also states the physical state of each species and the enthalpy change for the amounts of reactants and products shown exactly as written. Because enthalpy is extensive, it scales with the quantities in the equation, so doubling all coefficients doubles the enthalpy change. Reversing a reaction changes the sign of delta H, since the energy absorbed in one direction is released in the other. The physical states matter because melting, vaporizing or dissolving a substance absorbs or releases additional enthalpy. Thermochemical equations are the working format for stoichiometric energy calculations in chemistry.
Going deeper: Thermochemical Equation
Key ideas: Read the equation as a statement about moles: a delta H of minus 572 kJ for the equation as written means per two moles of water formed, not per mole. If you halve the coefficients you halve the enthalpy. State symbols are part of the equation, because liquid and gaseous water differ by 44 kJ per mole.
Common mistakes and connections: Beginners often copy delta H unchanged when scaling or reversing a reaction. Also, the equation does not tell you how fast the reaction is. It is the working format for Hess's law and for stoichiometric heat calculations, such as how much heat is released burning a given mass of fuel.
Visualization of Thermochemical Equation
2H2(g) + O2(g) gives 2H2O(l) with delta H = -572 kJ, so one mole of water corresponds to -286 kJ. Coefficients, states and delta H go together. The interactive lesson shows this as a live animation or chart.
Worked example and use case
2H2(g) + O2(g) -> 2H2O(l) with delta H = -572 kJ, which is the enthalpy for forming two moles of liquid water.
Frequently asked questions about Thermochemical Equation
What is Thermochemical Equation?
A balanced equation that includes the enthalpy change for the stated amounts.
Is Thermochemical Equation a beginner, intermediate or advanced topic?
Thermochemical Equation is a beginner topic in Thermodynamics & Energetics. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Thermochemical Equation?
Study these earlier topics in Thermodynamics & Energetics first: Calorimetry, Bomb Calorimeter, Coffee-Cup Calorimeter.
What comes after Thermochemical Equation?
The next topics in Thermodynamics & Energetics are Standard Enthalpy of Formation and Standard State.
Can I practise Thermochemical Equation with quizzes?
Yes. The interactive lesson includes a self-check question on Thermochemical Equation, and the Thermodynamics & Energetics quiz draws on every topic in this area.
Where Thermochemical Equation fits in Thermodynamics & Energetics
Thermochemical Equation is topic 18 of 91 in Thermodynamics & Energetics.