4: Gases Flashcards
What is pressure and what is its unit?
Pressure measures the normal (perpendicular) force exerted on a surface per unit area. It is measured in pascal (Pa).
What is the formula for pressure?
Pressure=normal force on a surface/area of the surface=F/A
1Pa=?N
1Pa=1N M^-2 (newton per square meter)
What is atmostpheric pressure?
Atmospheric pressure is the force from the atmosphere around us, which acts on all surfaces exposed to the atmosphere, including our bodies.
What is the unit for atmospheric pressure and what is its relationship with Pa?
atm, 1atm=100 kPa=atmospheric pressure at sea level
What tool is used to measure gas pressure and how does it work?
Bourdon gauge. It has a curved metal tube which uncoils when pressure is applied, which moves the pointer around a dial.
What is Boyle’s law?
Boyles’ Law states that for any gas with a fixed mass and temperature, its pressure is inversely proportional tro its volume
If the pressure of a gas becomes k times the original pressure, and the temperature stays constant, what is the new volume of the gas in relation to the original volume?
The volume will become 1/k of the original volume.
What is the shape of a graph plotted against the pressure and temperature of a gas? Where does the graph cut the x-axis (temperature axis)?
It is a linear graph with x-intercept at -273.15°C (absolute zero).
What is the kelvin temperature scale in relation with the celcius temperature scale?
273 kelvin=0°C, 0 kelvin=-273°C
What is another name for the kelvin temperature scale? Why?
It is also called absolute temperature scale, because 0 kelvin=absolute zero
What is the pressure law?
For a gas with fixed volume and mass, its pressure is directly proportional to its kelvin temperature.
What is the shape of a graph plotted against the volume and temperature of a gas? Where does the graph cut the x-axis (temperature axis)?
It is a linear graph with x-intercept at -273.15°C (absolute zero)
What is Charles’ law?
Charles’ law shows that for a gas with fixed mass and pressure, its volume is directly proportional to its kelvin temperature.
What can be inferred from Boyle’s law, the pressure law, and Charles’ law?
The product of the pressure of a gas and its volume is directly proportional to its temperature, or pV/T=constant.
How many molecules are there in a mole?
6.02*10^23 (Avogadro’s number)
What is the general gas law?
pV=nRT, where n is the number of moles of molecules in a gas
What is R in the general gas law?
R is called the universal gas constant, which is found to be 8.31 J mol^-1 K^-1
What is an ideal gas and how can a real gas behave like an ideal gas?
An ideal gas is a gas that oberys the general gas law. A real gas behaves like an ideal gas at low pressures and high temperatures.
What does the kinetic gas theory state?
Gas molecules are in random motion all the time.
What are the assumptions of molecules in an ideal gas?
- All molecules have the same mass and are identical.
- All molecules are in continuous random motion.
- There is a large number of molecules in the container.
- The size of the molecules are negligible compared with the separation between them.
- The duration of collisions are negligible compared with the time between collisions.
- The collisions of the molecules themselves/with the container are perfectly elastic.
- Intermolecular forces are negligible.
In which conditions do the gas satisfy the assumptions of the ideal gases?
When the temperature is high (well above its boiling point) and pressure is low.
What is the change in gas pressure when there is a change in momentum?
When there is a higher momentum, the gas pressure increases.
What is the relationship between pressure, volume, mass, and velocity in an ideal gas?
pressurevolume=1/3mass*mean square value of velocities
pV=1/3Nm(msv.c^2)
What is the total kinetic energy in one mole of gas?
3/2RT
What is the average kinetic energy of a molecule?
3RT/2Na(where Na denotes the number of molecules in one mole of gas)
Why can we infer the amount of total KE of gas molecules from their temperature?
Shown from the equation KEavg=3RT/2Na, temperature (in kelvin) is directly proportional to the average KE.
What is the molecular potential energy for ideal gases? What does this tell about the total internal energy of an ideal gas?
There is no potential energy for an ideal gas from the assumptions. Therefore, the total internal energy of an ideal gas is given by its total kinetic energy=3/2nRT.
What is the root mean square speed of gas molecules and how can it be caluclated?
The root-mean-square speed (rms) is the typical speed of molecules, calculated by taking the square root of (msv.c^2). rms.c=sqrt(3pV/Nm)=sqrt(3RT/mNa)
What is Nm and mNa in calculating the rms.c?
Nm: total mass of the gas
mNa: molar mass of the gas
How can a mechanical simulator simulate Boyle’s law?
When the voltage is unchanged, and when the weight of the piston is increased, the height of the piston decreases, which simulates what happens when the temperature is constant but the pressure increases. This results in a decrease in volume, simulating Boyle’s law.
How can a mechanical simulator simulate the pressure law?
When the voltage is increased, and the height of the piston is unchanged, the weight of the piston increases, which simulates what happens when the temperature rises and the volume stays constant. This results in an increase in pressure, simulating the pressure law.
How can a mechanical simulator simulate Charles’ law?
When the voltage is increased, and the weight of the piston is unchanged, the height of the piston increases, which simulates what happens when the temperature rises and the pressure stays constant. This results in an increase in volume, simulating the Charles’ law.
How can a mechanical simulator simulate the relationship between volume and the number of molecules?
When the voltage and weight of the piston ar eunchanged, but more ball bearings are added to the simulator, the height of the piston increases, which simulates what happens when the temperature and pressure is constant but more gas molecules are added. This results in an increase in volume, simulating the relationship between volume and the number of molecules.
