Thermodynamic systems and energy accounts
Введено| English | Значение |
|---|---|
| internal energy/ɪnˈtɜːnl ˈenədʒi/ | внутренняя энергия |
| adiabatic/ˌædiəˈbætɪk/ | адiabатный |
What would explain this observation?
- Compressing a gas can warm it even without a heater. Work is another path for energy transfer into the system.
Build the model
- Internal energy 内能 is a property of the chosen system.
- Heat and work describe energy transfer across its boundary.
- For an ideal monatomic gas, internal energy depends on temperature and amount.
- adiabatic 绝热的: A process with no heat transfer.
- internal energy: Total microscopic kinetic and potential energy of a system.
In this convention, what happens during adiabatic compression?
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
Adiabatic means no heat transfer (Q = 0). In compression the surroundings do work on the gas, and with Q = 0 that work raises the internal energy. Work done BY the gas is negative in compression under this convention.
Match each technical term to its precise meaning.
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- State a sign convention before using the first law.
- Here change in internal energy equals heat into the system minus work done by the system.
- Expansion work can reduce internal energy when no heat enters.
In the lab: Identify whether a process is isothermal, adiabatic or at constant volume. On a pressure-volume graph, area under the process curve gives work done by the gas. The path matters for work even when endpoints match.
Which two habits make the investigation or model in this case more defensible?
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: gas gains 300 J by heating and does 120 J of work.
- With ΔU = Q-W, ΔU = 300-120 = 180 J.
- For adiabatic compression, Q=0 and work done by the gas is negative, so ΔU is positive.
Your turn: A gas gains 500 J of heat and does 200 J work. Find internal-energy change.
A gas gains 500 J of heat and does 200 J work. Find internal-energy change.
Сложность 2/5 · 140 монет + небольшой бонус за первое выполнение сегодня
The result is 300 J. Known: heat gained Q = 500 J; work done by the gas W = 200 J. Use the stated convention delta U = Q - W. Delta U = 500 - 200 = 300 J. The internal energy rises by 300 J because more energy entered as heat than left as work.
Check the conclusion and its limits
- Adiabatic does not mean constant temperature.
- Use the stated sign convention; some courses write work done on the gas with the opposite sign.
Not true: Every adiabatic process has constant temperature. Adiabatic fixes heat transfer (Q = 0), not temperature. An adiabatic compression raises temperature - bicycle pumps warm up - and an adiabatic expansion lowers it. Isothermal, not adiabatic, is the constant-temperature process.
- Internal energy is a property of the chosen system.
- State a sign convention before using the first law.
- Watch for: adiabatic does not mean constant temperature.
Write from an internal-energy change of 450 J
- A gas gains 800 J of heat and does 350 J of work.
- Find the change in internal energy. Adiabatic means no heat transfer, not constant temperature.
Adiabatic fixes heat transfer (Q = 0), not temperature.
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
True. Adiabatic fixes heat transfer (Q = 0), not temperature. An adiabatic compression raises temperature - bicycle pumps warm up - and an adiabatic expansion lowers it. Isothermal, not adiabatic, is the constant-temperature process.
A process with no heat transfer: write the technical term.
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
adiabatic means A process with no heat transfer.
A gas gains 800 J of heat and does 350 J of work. What is the change in its internal energy, and why is an adiabatic process not automatically isothermal?
With the sign convention that work is done by the gas, the internal-energy change is heat in minus work out.
What is the change in internal energy?
Сложность 1/5 · 100 монет + небольшой бонус за первое выполнение сегодня
800 minus 350 is 450 J. Other options — 300 J (the lesson change for 500 J of heat and 200 J of work); 800 J (the heat gained).