heat of reaction
C2Technical/Scientific
Definition
Meaning
The amount of heat energy released or absorbed during a chemical reaction at constant pressure.
In thermodynamics, it refers specifically to the enthalpy change (ΔH) of a reaction, indicating whether the process is exothermic (releases heat) or endothermic (absorbs heat).
Linguistics
Semantic Notes
Always used as a singular noun phrase; typically measured in joules or calories per mole; central concept in thermochemistry.
Dialectal Variation
British vs American Usage
Differences
No significant lexical differences; both use identical terminology.
Connotations
Identical scientific connotations in both varieties.
Frequency
Equally frequent in academic/technical contexts in both regions.
Vocabulary
Collocations
Grammar
Valency Patterns
The heat of reaction for [chemical process] is [value].We determined the heat of reaction by [method].[Compound] has a heat of reaction of [measurement].Vocabulary
Synonyms
Strong
Neutral
Weak
Vocabulary
Antonyms
Phrases
Idioms & Phrases
- “No common idioms exist for this technical term.”
Usage
Context Usage
Business
Rare, except in chemical/pharmaceutical industry R&D reports.
Academic
Core term in chemistry, chemical engineering, and materials science textbooks and research.
Everyday
Virtually never used in casual conversation.
Technical
Essential terminology in laboratory reports, process design, safety data sheets, and thermodynamic calculations.
Examples
By Part of Speech
verb
British English
- The reaction heats the solution considerably.
- We need to heat the mixture to initiate the reaction.
American English
- The compound heats up during decomposition.
- You must heat the reactants to achieve ignition.
adverb
British English
- The mixture reacted heatily, producing steam.
- The process runs thermally efficient.
American English
- The compound decomposes heatedly under pressure.
- The system operates heat-efficiently.
adjective
British English
- The heating effect was measured precisely.
- A heat-related parameter is crucial for safety.
American English
- The heating process is exothermic.
- Heat-sensitive materials require careful handling.
Examples
By CEFR Level
- Chemical reactions can make things hot or cold.
- Burning wood gives off heat.
- Some reactions release heat, others absorb it.
- Scientists measure the heat change in reactions.
- The heat of reaction indicates whether a process is exothermic or endothermic.
- We calculated the heat of reaction using calorimetry.
- The standard heat of reaction for the combustion of methane is -890 kJ mol⁻¹.
- Determining the enthalpy change of reaction is fundamental to process design.
Learning
Memory Aids
Mnemonic
Think: HEAT tells you if the REACTION eats energy (endothermic) or emits energy (exothermic).
Conceptual Metaphor
Chemical energy as a fluid that flows out of or into a reaction vessel.
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- Avoid literal translation as 'жар реакции' (which implies emotional heat). Correct term: 'теплота реакции' or 'энтальпия реакции'.
Common Mistakes
- Using 'heat' alone instead of the full phrase 'heat of reaction'.
- Confusing it with activation energy.
- Forgetting to specify per mole basis when giving numerical values.
Practice
Quiz
What does a negative heat of reaction signify?
FAQ
Frequently Asked Questions
No, heat of reaction is an extensive property (depends on amount), while temperature change is intensive. Heat of reaction causes temperature change in a system.
Yes, for thermoneutral reactions where no net heat is exchanged, ΔH = 0.
It determines energy requirements for reactors, cooling/heating loads, safety measures, and process economics.
Typically using a calorimeter, which isolates the reaction and measures temperature changes to calculate enthalpy change.