Week 9 Chap 10 intermolecular forces: gases Flashcards
Distinctive properties of gases
Gasses have indefinite volume and shape;
Gasses can exert pressure;
Volume of gas assumes its container; and
Low density;
The standard atmospheric pressure
The standard atmospheric pressure (atm) is the pressure exerted by a column of mercury 760 mm high at sea level at a temperature of 273.15 K (0 °C).
The SI units for pressure is the pascal (Pa) which is defined as one Newton per square metre. 1 atm = 101,325 Pa, or 101.3 kPa.
1 atm = 760 torr = 760 mm Hg
Standard temperature and pressure
tandard temperature is 273.15 K (0 °C).
Standard pressure is 1 atm or 760 torr or 760 mm Hg or 101.325 kPa.
At STP, one mole of gas occupies 22.4 L of volume (molar volume).
Kelvin scale in gas laws
As volume decreases with temperature, there will be a temperature at which V = 0. Kelvin identified this temperature to be -273.15 °C which is called absolute zero. Therefore, the Kelvin scale must be used because zero on the Kelvin scale corresponds to a complete stop of molecular motion.
Boyles law
Boyle’s law states that “the volume of a fixed amount of gas maintained at constant temperature is inversely proportional to the gas pressure” (V∝1/P)
Charles Law
Charles’ law states that ‘the volume of a fixed amount of gas maintained at constant pressure is directly proportional to the Kelvin temperature of the gas (V∝T)
Gay-Lussac’s Law
Gay-Lussac’s law (Amontons’s law) describes that the pressure of a fixed amount of gas is directly proportional to the Kelvin Temperature of the gas when the volume is kept constant (P∝T).
Combined gas law
Using the mathematical expressions from the previous three gas laws, the P, V, and T Relationships for a given mass of any gas may be expressed as a single equation PV/T = constant.
Avogadros Law
Avogadro determined that “at the same temperature and pressure, equal volumes of different gases contain the same number of molecules”.
Avogadro’s Law describe that the volume (V) of gas is proportional to the number of moles (n) of gas at constant temperature and pressure (V∝n).
Daltons law
Dalton’s law states that ‘the total pressure of a mixture of gases is just the sum of the pressures that each gas would exert if it were present alone’
Ptotal = Pgas1 + Pgas2 +Pgas3
Ideal gas law
Molecules in an ideal gas have its own molar mass
Molecules in an ideal gas have kinetic energy
Molecules in an ideal gas collide each other and their interactions are perfectly elastic
Molecules in an ideal gas exert pressure due to the collision of the gas molecules with the wall of container
Molecules in an ideal gas have no attractive forces
Molecules in an ideal gas have no repulsive forces
There are over 15 different ideal gas constants depending on the units. However, The common one in SI unit is 8.314 J·K-1·mol-1 (J/mol·K) or 8.134 L·kPa·mol-1·K-1.
The kinetic molecular theory
Gases consist of tiny particles.
The distance between particles is large compared with the size of the particles themselves. The volume occupied by a gas consists mostly of empty space.
Gas particles have no attraction for one another.
Gas particles move in straight lines in all directions, colliding frequently with one another and with the walls of the container.
No energy is lost by the collision of a gas particle with another gas particle or with the walls of the container. All collisions are perfectly elastic.
The average kinetic energy for particles is the same for all gases at the same temperature, and its value is directly proportional to the Kelvin temperature.
The kinetic energy (KE) of a particle is expressed by the equation: KE = ½mv2 , where m is mass of gas particle and v is speed of gas particle
Effusion and diffusion of gases
Effusion is the movement of a gas into a vacuum.
The effusion rate of a gas is inversely proportional to its molar mass.
The lighter the gas molecules, the faster the effusion through pin holes.
Diffusion is a mixing of two or more gases.
Average rate of movement is dependent on temperature and molar mass
Similar to effusion, diffusion is faster for smaller gas molecules than larger/heavier gas molecules
The segments in the picture represent a gas molecule collisions with other gas molecules during the travel from Start to End
behaviour of ideal gases in changing conditions
Increasing ngas while Vgas constant = increase in pressure by providing more gas particles to collide onto the wall of the container
Decreasing Vgas while keeping ngas constant = increase in the pressure by reducing the size of the wall.
Increasing T while Vgas and ngas constant = increase in pressure by providing kinetic energy to the gas particles so the particles move faster.
Real gases
In ideal gases, it is assumed that there are no interactions between the gas particles. However, in real gases, there are weak attractive forces operating between the particles that cause them to behave in a non-ideal way. These weak forces are known as intermolecular forces. In general, the deviations from ideal gas behaviour increase 1. as temperature decrease and 2. as pressure increase
