C15 Ideal Gases Flashcards
What is 1 Pa equal to?
1Pa = 1Nm^-2
How does a Gas Exert a Pressure?
-Gas consists of molecules in constant random motion.
-When a molecule collides with surface it undergoes a momentum change as it reverses direction.
-By Newton’s 2nd and 3rd laws, the surface therefore experiences a force from the colliding molecule.
-Pressure exerted by gas is equal to total force exerted by the molecules on a unit area of the surface
-P = F / A (where F is the force perpendicular to the surface area).
Assumptions about Ideal Gases and Kinetic Theory: (6)
1) Molecules are points- the vol of molecules is insignificant compared to vol of the ideal gas.
2) Molecules don’t attract each other- if they did then pressure exerted by the gas on its container would reduce.
3) All collisions between gas molecules and their container are elastic- no loss in KE.
4) Time taken for a collision is much shorter than the time between collisions.
5) Any sample of an ideal gas contains a very large no. of molecules.
6) The molecules in a gas have constant random motion.
How can the amount of a substance be measured?
Amount of a substance, can be measured in the SI base unit of the mole.
What’s one mole?
One mole is the amount of substance containing 6.02×10^23 particles (atoms or molecules).
What is Avogadro’s Constant (Na)?
Avogadro’s constant (Na), is equal to no. of atoms in exactly 12g of the isotope carbon 12.
What’s the equation for calculating the number of molecules in a substance?
The no. of particles (molecules) in a substance, determined by multiplying no. of moles of the substance by Avogadro’s constant:
N = n x Na
What is the Molar Mass of a substance?
Molar mass of a substance = mass of one mole of the substance.
Equation used for Molar Mass?
M= m / n
-m is the mass of the substance,
-M is the molar mass (in grams, which is the same as the nucleon number for the atom/molecule) of the particles that make up the substance.
-n, the no. of moles.
What does the experimental gas laws state?
These state how the pressure (p), vol (V) and the absolute temp (T) of an ideal gas relate to each other.
Real gases at relatively low pressures and well above their condensation temp behave like…
an ideal gas.
Boyle’s Law states:
Boyle’s law states that the pressure exerted by a fixed amount of gas is inversely proportional to its volume at a constant temperature.
What is the equation, For a fixed mass of gas at a constant temp:
pV = constant
Ideal Gas
Ideal gas, defined as gas that obeys Boyle’s law at all pressures.
Equation for when a gas changes pressure from p1 to p2 while undergoing a vol change from V1 to V2:
p1 x V1 = p2 x V2
Why is it Real Gases do not obey Boyle’s Law at very high pressures?
Because as pressure increase the vol decreases exponentially resulting gas to condense and molecules eventually attract each other, breaking the ideal gas assumptions.
-By plotting p vs 1/V we get straight line graphs for each temp. A change in temp would effect what?
The gradient (represents the constant), as increase in temp = increase in pressure.
For pressure laws temperature must always be in what units?
Kelvin
Pressure Law:
For a fixed mass of gas at a constant volume:
P / T = constant
When a gas changes pressure from p1 to p2 while undergoing a temp change from T1 to T2:
p1 / T1 = p2 / T2
Charles’ Law:
For a fixed mass of gas at a constant pressure,
V / T = constant
When a gas changes volume from V1 to V2 while undergoing a temp change T1 to T2:
V1 / T1 = V2 / T2
-Temperature must always be in Kelvin
The Ideal Gas Equation:
Combining all three gas laws for a constant mass of gas gives,
pV / T = constant
constant = n x R (n, no. of mols and R, molar gas constant, 8.31)
Therefore pV = nRT
p1V1 / T1 = p2V2 / T2
(Temp in Kelvin)
We know N = n x Na
Therefore pV = (N / Na) x RT
Rearrange to get pV = (R / Na) x NT
Boltzmann constant, k = R / Na
Where k is another constant, 1.38 x 10^-23
And so ideal gas equation can be written as pV = kNT (N, the no. of molecules).
What does the Kinetic Theory of Gases state:
Kinetic Theory of gases- states a gas consists of point molecules moving about in random motion.
How does the pressure of a gas alter with if the volume in the container decreases?
Volume: if vol container decreases, greater no. molecules hitting inside container per sec.
Greater force exerted, pressure increases.
How does the pressure of a gas alter with if the temperature in the container increases?
Temperature: if temp of container increases, molecules moving greater speeds, more hitting inside container per sec and will each exert greater force (Newton’s 2nd Law).
