When to use this calculator
Apply the first law of thermodynamics with an explicit work-sign convention. Uses the convention ΔU=Q−W, where W is work done by the system.
Explore the heat & thermal change calculators for other questions in this topic. For a related calculation, use the Heat Conduction Calculator: Find steady heat-transfer power through a uniform flat layer.
PUTTING IT INTO PRACTICE
First Law Heat: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Internal energy change (J) | 100 |
| Work done by system (J) | 50 |
| Result | 150 J |
- Check the input labels and enter the example values above.
- Apply the relationship: Heat added to system = internal energy change + work done by system.
- The result is 150 J, rounded for display.
How to interpret your result
Uses the convention ΔU=Q−W, where W is work done by the system.
Heating within a phase uses specific heat; phase changes use latent heat. Material properties vary with temperature. Ideal conduction calculations omit several real-world heat-transfer paths.
Frequently asked questions
Does heating energy include boiling automatically?
No. Energy to reach a boiling temperature and latent energy to vaporise liquid are separate contributions.
When is the first law heat calculator useful?
Apply the first law of thermodynamics with an explicit work-sign convention. Uses the convention ΔU=Q−W, where W is work done by the system.
How do I use the first law heat calculator?
Enter internal energy change (j), work done by system (j). The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Heat added to system = internal energy change + work done by system.
What should I check before using the result?
Uses the convention ΔU=Q−W, where W is work done by the system.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see OpenStax: thermal expansion ↗. This is a topic reference, not an external review or endorsement of this tool.
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