G & P : GASEOUS STATE & LAWS Flashcards
What are the three states in which most substances can exist?
Solid, Liquid Gas
What characterizes gases compared to liquids and solids?
- Gases lack a definite shape
- doesnβt have occupy a specific volume
**- Molecular motion is totally random
- Each molecule moves freely and independently of other molecules (forces of attraction is negligible) ** - easier to predict the behaviour of gases when subjected to changes in temperature and pressure
(Liquid molecules touch each other but can freely move, solids are in fixed positions in crystal lattice)
What is the kinetic molecular theory?
Kinetic molecular theory states that gas particles are in constant motion and exhibit perfectly elastic collisions.
What is meant by the expansibility of gases?
- gases have limitless expansion capabilities. They expand to fill the whole vessel in which they have been placed in.
How do gases exert pressure?
- the pressure is exerted uniformly on the walls of the container in all directions
What are the general characteristics of a gas?
- Expansibility
- Pressure
- Compressibility
4.Diffusibility
5.Effect of heat
What property of gases allows them to be compressed?
- Compressibility
What happens to a gas when it is heated in a confined space?
- pressure and volume of the gas increases
What are the four measurable properties of a gas?
1.Volume
2.Pressure
3.Temperature
4.Number of particles
In what units is gas volume typically measured?
1 L = 1000ml
1ml = 1 cm^3
m^3
How is gas pressure commonly expressed?
1 Pa = 1 N/m^2
1 bar = 105 Pa = 0.1MPa
1 atm = 760mmHg = 760 Torr = 101 325 Pa = 101.325kPa
I mmHg = 1 Torr
What temperature scale is used in gas calculations?
K = C + 273
How can the number of moles of a gas be determined?
Divide the mass of the gass by its molar mass.
State Boyleβs Law.
Boyles law; π πΌ 1/π (constant n and T)
PV = constant
For a fixed amount of gas at constant temperature, the volume is inversely proportional to pressure.
State Charlesβs Law.
Charles law; π πΌ π (constant n and P)
V/T = constant
For a fixed amount of gas at constant pressure, the volume of the gas is directly proportional to the absolute temperature of the gas.
State Avogadroβs Law.
Avogadro law; π πΌ π (constant P and T)
V/n = constant
constant = molar volume
At constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of the gas present.
- molar volumes of all gases are approximately the same (22.414 L at 0 degrees C and 1 amt, 22.711 L at STP)
What is the ideal gas equation?
The three laws are combined into a single law called the ideal gas law.
V πΌ ππ/π
ππ = ππππ π‘πππ‘ Γ ππ
When the constant of proportionality is written as R, this expression becomes the ideal gas law:
ππ = ππ
π β¦ β¦ β¦ β¦ β¦ β¦ . πΈππ’ 4
What does the gas constant ( R ) represent in the ideal gas equation?
The numerical value of R depends on the units of pressure, volume, and temperature:
R=8.314J/(molβ
K) (when using SI units: pressure in pascals, volume in cubic meters, temperature in kelvins)
**R=0.0821Lβ
atm/(molβ
K) **(when pressure is in atmospheres, volume in liters, and temperature in kelvins) at STP
Physical Interpretation:
It represents the energy per mole per kelvin required for the ideal gas to maintain its properties.
Universal Nature:
R is a universal constant, meaning its value is the same for all ideal gases, as it is derived from fundamental constants of nature.
How can the ideal gas equation be used to calculate molar mass?
n = m/M
PV = m/M RT
How can the ideal gas equation be used to calculate molar volume?
V(m) = V/n
V/n = RT/P
V(m) = RT/P
How is gas density determined using the ideal gas law?
density = m /V
Ο at STP = M/V(m)
n = m/M
PM = Ο RT
Ο = PM/RT
What is Daltonβs Law of Partial Pressure?
The total pressure of a mixture of gases is egual to the sum of the partial pressures of the individual gases present.
P(t) = P(A) + P(B)
P(t) = P(dry air) - P(water vapor)
P(t) = n(t) * RT / V
n(t) = n1 + n2 + n3
Differentiate Standard ambient Temperature and Pressure (SATP) and Standard Temperature and Pressure (STP)
SATP
25C (298.15K)
1 Bar = 105Pa
molar volume - 24.79L/ mol
STP
0C (273.15K)
1 atm = 101, 325 Pa
molar volume - 22.41L/ mol
why was pressure and volume correction necessary as seen in Van der Waals equation ?
The pressure and volume corrections in the Van der Waals equation account for the deviations of real gases from ideal gas behavior. These deviations occur due to the finite size of gas molecules and the intermolecular forces present in real gases.
Explain the volume correction
- Volume Correction (b)
Cause: Gas molecules occupy a finite volume, so the actual volume available for movement (free volume) is less than the measured volume V.
Correction: The term nb subtracts the volume occupied by the gas molecules themselves. Here:
b:* Proportional to the size of the gas molecules* (molar volume of the gas molecules).
n: Number of moles of gas.
Thus, Vβnb represents the effective volume available for the gas particles to move.
Explain pressure correction
- Pressure Correction ()
Cause: Real gas molecules experience intermolecular attractive forces, which reduce the force of collisions against the walls of the container. This lowers the observed pressure compared to what is predicted for an ideal gas.
Correction: To account for this, we add a: Proportional to the strength of intermolecular attractions.
: Represents the square of the number density of gas particles because intermolecular attractions depend on how closely packed the molecules are.
formula
What is Van der Waals Equation?
# Van der Waals Equation: (P + (a * n^2) / V^2) * (V - n * b) = n * R * T Where: # P = Pressure of the gas # V = Volume of the gas # n = Number of moles of the gas # T = Temperature of the gas (in Kelvin) # R = Ideal gas constant # a = Constant accounting for intermolecular forces # b = Constant accounting for the finite size of gas molecules
