Gas models and absolute temperature
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| absolute temperature/ˈæbsəluːt ˈtemprɪtʃə/ | nhiệt độ tuyệt đối |
| ideal gas/aɪˈdɪəl ɡæs/ | khí lý tưởng |
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
- In a gas model, particles move randomly and pressure results from momentum transfer at walls.
- The ideal gas 理想气体 equation connects pressure, volume, amount and absolute temperature.
- absolute temperature: Temperature on the kelvin scale.
- ideal gas: A gas model with specified simplifying assumptions.
Which scale belongs in a gas-law temperature ratio?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Gas-law ratios rest on absolute temperature measured from absolute zero, so kelvin is required. Celsius shifts the zero by 273.15 and breaks every ratio, even though a temperature DIFFERENCE is the same size in both scales.
Match each technical term to its precise meaning.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- At fixed amount and volume, pressure is proportional to kelvin temperature.
- At fixed temperature and amount, pressure is inversely proportional to volume.
- State which quantities are fixed before choosing a relationship.
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?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
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: pressure is 100 kPa at 300 K, with fixed volume and amount.
- At 330 K, p2/p1=T2/T1. p2=p1 T2/T1=100×330/300=110 kPa.
- A 30 °C rise is a 30 K change, but the temperature ratio must use kelvin.
Your turn: At fixed volume, pressure is 120 kPa at 300 K. Find pressure at 350 K.
Gas pressure uses kelvin temperature
$\frac{p_2}{p_1}=\frac{T_2}{T_1}\frac{V_1}{V_2}$
For a fixed amount of ideal gas, pressure rises with kelvin temperature and falls as volume increases.
At fixed volume, pressure is 120 kPa at 300 K. Find pressure at 350 K.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The result is 140 kPa. Known: p1 = 120 kPa at T1 = 300 K, fixed volume and amount; T2 = 350 K. Use p2/p1 = T2/T1. Rearranging: p2 = p1 x T2/T1 = 120 x 350/300 = 140 kPa. The ratio works only because both temperatures are in kelvin.
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: A gas pressure ratio can always use Celsius temperatures. Ratios of temperatures are meaningful only from absolute zero. 300 K to 350 K is a ratio of 350/300; the same temperatures in Celsius, 27 and 77, give 77/27 - a different, wrong answer.
- In a gas model, particles move randomly and pressure results from momentum transfer at walls.
- At fixed amount and volume, pressure is proportional to kelvin temperature.
- Watch for: an ideal gas is a model with conditions of validity.
Write from a pressure of 180 kPa
- At fixed volume, the pressure is 150 kPa at 250 K.
- Find the pressure at 300 K. The ratio must use kelvin.
A gas pressure ratio can always use Celsius temperatures.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Ratios of temperatures are meaningful only from absolute zero. 300 K to 350 K is a ratio of 350/300; the same temperatures in Celsius, 27 and 77, give 77/27 - a different, wrong answer.
Temperature on the kelvin scale: write the technical term.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
absolute temperature means Temperature on the kelvin scale.
At fixed volume and amount, the pressure is 150 kPa at 250 K. What is the pressure at 300 K, and why must the ratio use kelvin?
At fixed volume, pressure is proportional to kelvin temperature. Both temperatures in the ratio must be absolute.
What is the pressure at 300 K?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
150 times 300 divided by 250 is 180 kPa. The worked example starts at 100 kPa and 300 K. Other options — 150 kPa (the starting pressure); 110 kPa (the worked example's result).