G & P : GASEOUS STATE & LAWS

Question 1

What are the three states in which most substances can exist?

Answer 1

Solid, Liquid Gas

Question 2

What characterizes gases compared to liquids and solids?

Answer 2

• Gases lack a definite shape
• doesn’t 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)

Question 3

What is the kinetic molecular theory?

Answer 3

Kinetic molecular theory states that gas particles are in constant motion and exhibit perfectly elastic collisions.

Question 4

What is meant by the expansibility of gases?

Answer 4

• gases have limitless expansion capabilities. They expand to fill the whole vessel in which they have been placed in.

Question 5

How do gases exert pressure?

Answer 5

• the pressure is exerted uniformly on the walls of the container in all directions

Question 6

What are the general characteristics of a gas?

Answer 6

1. Expansibility
2. Pressure
3. Compressibility
   4.Diffusibility
   5.Effect of heat

Question 7

What property of gases allows them to be compressed?

Answer 7

• Compressibility

Question 8

What happens to a gas when it is heated in a confined space?

Answer 8

• pressure and volume of the gas increases

Question 9

What are the four measurable properties of a gas?

Answer 9

1.Volume
2.Pressure
3.Temperature
4.Number of particles

Question 10

In what units is gas volume typically measured?

Answer 10

1 L = 1000ml
1ml = 1 cm^3
m^3

Question 11

How is gas pressure commonly expressed?

Answer 11

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

Question 12

What temperature scale is used in gas calculations?

Answer 12

K = C + 273

Question 13

How can the number of moles of a gas be determined?

Answer 13

Divide the mass of the gass by its molar mass.

Question 14

State Boyle’s Law.

Answer 14

Boyles law; 𝑉 𝛼 1/𝑃 (constant n and T)
PV = constant
For a fixed amount of gas at constant temperature, the volume is inversely proportional to pressure.

Question 15

State Charles’s Law.

Answer 15

Charles law; 𝑉 𝛼 𝑇 (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.

Question 16

State Avogadro’s Law.

Answer 16

Avogadro law; 𝑉 𝛼 𝑛 (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)

Question 17

What is the ideal gas equation?

Answer 17

The three laws are combined into a single law called the ideal gas law.
V 𝛼 𝑛𝑇/𝑃
𝑃𝑉 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 × 𝑛𝑇
When the constant of proportionality is written as R, this expression becomes the ideal gas law:
𝑃𝑉 = 𝑛𝑅𝑇 … … … … … … . 𝐸𝑞𝑢 4

Question 18

What does the gas constant ( R ) represent in the ideal gas equation?

Answer 18

The numerical value of R depends on the units of pressure, volume, and temperature:

R=8.314J/(mol⋅K) (when using SI units: pressure in pascals, volume in cubic meters, temperature in kelvins)
**R=0.0821L⋅atm/(mol⋅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.

Question 19

How can the ideal gas equation be used to calculate molar mass?

Answer 19

n = m/M
PV = m/M RT

Question 20

How can the ideal gas equation be used to calculate molar volume?

Answer 20

V(m) = V/n
V/n = RT/P
V(m) = RT/P

Question 21

How is gas density determined using the ideal gas law?

Answer 21

density = m /V
ρ at STP = M/V(m)
n = m/M
PM = ρ RT
ρ = PM/RT

Question 22

What is Dalton’s Law of Partial Pressure?

Answer 22

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

Question 23

Differentiate Standard ambient Temperature and Pressure (SATP) and Standard Temperature and Pressure (STP)

Answer 23

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

Question 24

why was pressure and volume correction necessary as seen in Van der Waals equation ?

Answer 24

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.

Question 25

Explain the volume correction

Answer 25

1. 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, V−nb represents the effective volume available for the gas particles to move.

Question 26

Explain pressure correction

Answer 26

1. 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.

Question 27

formula

What is Van der Waals Equation?

Answer 27

# 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