Gas models and absolute temperature
แนะนำใหม่| English | ความหมาย |
|---|---|
| absolute temperature/ˈæbsəluːt ˈtemprɪtʃə/ | absolute temperature: อุณหภูมิสัมบูรณ์ |
| ideal gas/aɪˈdɪəl ɡæs/ | ideal gas: ก๊าซอุดมคติ |
What would explain this observation?
- A sealed gas container changes pressure when heated. Celsius ratios cannot predict the pressure change because the gas model uses absolute temperature 绝对温度.
Build the model
- Gas particles move randomly and collide with container walls.
- Pressure depends on collisions with the walls.
- At fixed temperature, compression reduces volume and increases pressure for a fixed amount of gas.
- absolute temperature: Temperature on the kelvin scale.
- ideal gas 理想气体: A gas model with specified simplifying assumptions.
For a fixed amount of gas at constant temperature, halving volume does what to pressure?
ความยาก 1/5 · 100 เหรียญ + โบนัสเล็กน้อยในการทำครั้งแรกวันนี้
At fixed temperature the gas particles keep their average speed, so halving the volume doubles how often they hit the walls - the pressure doubles (pV = constant). Halving the pressure would require the volume to double instead.
Match each technical term to its precise meaning.
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Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- State which quantities stay fixed.
- A pressure-volume relation requires consistent units and a fixed temperature.
- The kelvin-based temperature ratio is an extension only where the course explicitly specifies it.
In the lab: Use approved apparatus with a temperature range and pressure limit set by the teacher. Allow thermal equilibrium and record pressure against kelvin temperature. Never heat an improvised sealed vessel.
Which two habits make the investigation or model in this case more defensible?
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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 pressure is 100 kPa at volume 60 cubic centimetres, at fixed temperature. p1V1=p2V2.
- At volume 30 cubic centimetres, p2=p1V1/V2=100×60/30=200 kPa.
Your turn: At fixed temperature, pressure is 120 kPa at volume 50 cubic centimetres. Find pressure at volume 30 cubic centimetres.
Compressing a gas at constant temperature
$p_1V_1=p_2V_2$
For a fixed amount of gas at constant temperature, halving volume doubles pressure.
At fixed temperature, pressure is 120 kPa at volume 50 cubic centimetres. Find pressure at volume 30 cubic centimetres.
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The result is 200 kPa. Known: p1 = 120 kPa at V1 = 50 cubic centimetres, fixed temperature and amount; V2 = 30 cubic centimetres. Use p1V1 = p2V2. Rearranging: p2 = p1V1/V2 = 120 x 50/30 = 200 kPa. The smaller volume gives a proportionally higher pressure.
Check the conclusion and its limits
- An ideal gas is a model with conditions of validity.
- Celsius zero is not zero molecular motion, and internal energy is not determined by pressure alone.
Not true: At fixed temperature, halving gas volume halves its pressure. At fixed temperature pressure and volume are INVERSELY linked: pV = constant. Halving the volume doubles the pressure, so pressure moves in the opposite direction to volume, not the same direction.
- Gas particles move randomly and collide with container walls.
- State which quantities stay fixed.
- Watch for: an ideal gas is a model with conditions of validity.
Write from a pressure of 300 kPa
- At fixed temperature, the pressure is 150 kPa at a volume of 40 cubic centimetres.
- Find the pressure at 20 cubic centimetres. Halving the volume does not halve the pressure.
At fixed temperature, halving gas volume halves its pressure.
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At fixed temperature pressure and volume are INVERSELY linked: pV = constant. Halving the volume doubles the pressure, so pressure moves in the opposite direction to volume, not the same direction.
Temperature on the kelvin scale: write the technical term.
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absolute temperature means Temperature on the kelvin scale.
At fixed temperature, the pressure is 150 kPa when the volume is 40 cubic centimetres. What is the pressure at 20 cubic centimetres, and what does halving the volume do?
At fixed temperature, the first pressure times the first volume equals the second pressure times the second volume.
What is the pressure at 20 cubic centimetres?
ความยาก 1/5 · 100 เหรียญ + โบนัสเล็กน้อยในการทำครั้งแรกวันนี้
150 times 40 divided by 20 is 300 kPa. Halving the volume doubles the pressure.