The physical properties of a substance depends on the state of the substance. When a substance undergoes a change in state, many of its physical properties change.
Under certain condition of pressure & temp., most substances can exist in any one of the three state of matter.
E.g. water - solid :ice ; liquid : water ; gaseous : steam / water vapor
In gases - molecular motion is totally random, forces of interaction between molecules are so small, each molecules moves freely and essentially independently of other molecules.
SUBSTANCES THAT EXIST AS GASES
Under normal condition of pressure & temp. (1 atm , 25 o C), elements that exist as gases are:
A second type of barometer, a manometer has two arms, one opened to the atmosphere and one closed or connected to a container filled with gas. The pressure exerted by the atmosphere or by gas in a container is proportional to the difference in the mercury levels (h).
Charles’ Law states that : the vol. of a fixed amounts of a gas maintained at constant pressure is directly proportional to the absolute temp. of the gas.
Under 2 diff. sets of conditions for a given sample of gas at constant pressure :
V 1 / T 1 = k 2 = V 2 / T 2
V 1 / T 1 = V 2 / T 2
V 1 , V 2 are volumes of the gases at temp. T 1 , T 2 (both in kelvins).
V T V = k 2 T or V/T = k 2 k 2 is proportionality constant .
13.
The Volume – Amount Relationship : Avogadro,s Law
Amedeo Avogadro – complemented the studies of Boyle, Charles and Gay-Lussac. He published a hypothesis that stated :
At the same temp. and pressure, equal volumes of different gases contain the same number of molecules (or atoms if the gas is monatomic).
The volume of any given gas must be proportional to the number of molecules present;
V n
V = k 3 n where n represents the number of moles and
k 3 is the proportionality constant.
Avogadro’s Law – at constant pressure and temp., the vol. of a gas is
directly proportional to the number of moles of the gas present .
R, the proportionality constant is called the gas constant.
Ideal gas – a hypothetical gas whose pressure- volume-temp. behavior can be completely accounted for by the ideal gas equation. The molecules of an ideal gas do not attract or repel one another, and their vol. is negligible compared with the volume of the container.
To apply the ideal gas equation to a real system, we must evaluate the gas constant, R.
At 0 o C (273.15K) and 1 atm pressure, many real gas behave like an ideal gas. Exp. show that under these conditions, 1 mole of an ideal gas occupies 22.414L.
The conditions 0 o C (273.15K) and 1 atm pressure are called standard temp. and pressure (STP).
From PV = nRT
R = PV/nT
=( 1 atm)(22.414L) = 0.082057 L.atm/K.mol
(1 mol)(273.15K)
For most calculations, use R=0.0821 L.atm/K.mol and the molar volume of a gas at STP as 22.4L.
Molar Mass of a substance is found by examining its formula and summing the molar masses of its component atoms (if the actual formula of the substance is known).
For an unknown gaseous substance, an experiment is needed to determine the density value (or mass and volume data) at a known temp. and pressure.
A Balloon of volume 0.55mL at sea level at pressure P=1 atm is allowed to rise to a height with P=0.40atm. If the temperature remains constant, find the final volume of the balloon.
A 550mL of Fluorine gas, F 2 is heated from 22 C to 87 C at constant pressure.What is its final volume?
What is the volume of H 2 evolved when 1.20g of Mg react with excess of HCl at STP.
A helium filled balloon has a volume of 6.15m 3 at 14 C and 762mmHg. If its volume expands to 6.37m 3 and pressure falls to 749mmHg. Find its final temperature?
A sample of carbon monoxide gas has a volume of 3.20mL at 125 C. Calculate it temperature when its occupy 1.547mL at constant pressure.
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