键能计算器
利用键能数据估算化学反应的焓变。
kJ
kJ
Enthalpy Change (ΔH°)
-815.0 kJ
Enthalpy Change (ΔH°) vs Sum of ΔHf° (Products)
公式
Enthalpy Change of Reaction
Formula
ΔH°rxn = Σ ΔHf°(products) − Σ ΔHf°(reactants)
Where:
Negative ΔH means exothermic (releases heat). Positive ΔH means endothermic (absorbs heat).
计算示例
Combustion of methane: products ΔHf° sum = -890 kJ, reactants ΔHf° sum = -75 kJ.
- 01ΔH°rxn = Σ ΔHf°(products) - Σ ΔHf°(reactants)
- 02ΔH°rxn = -890 - (-75)
- 03ΔH°rxn = -890 + 75
- 04ΔH°rxn = -815 kJ (exothermic)
常见问题
What is enthalpy of formation?
The standard enthalpy of formation (ΔHf°) is the heat change when 1 mole of a compound forms from its elements in their standard states.
What is the ΔHf° of elements in their standard state?
By definition, ΔHf° = 0 for elements in their most stable form at standard conditions (e.g., O₂(g), C(graphite), Fe(s)).
How do I know if a reaction is exothermic?
If ΔH < 0, the reaction releases heat to the surroundings and is exothermic. If ΔH > 0, it absorbs heat and is endothermic.
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