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# Gases

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## Micaela Tan

on 16 March 2014

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#### Transcript of Gases

Gases
Introduction
Gas is one of the four fundamental states of matter.
It is a formless fluid that occupies space or enclosure and which can be changed to the liquid or solid state only by the combined effect of increased pressure and decreased temperature.

Properties of Gases
Measurable Properties of Gases
PRESSURE
AMOUNT OF GAS
When you pump air into a rubber tire, you increase the quantity of gas and also increase the pressure in the tire. In gas laws in a container is usually expressed in moles (n).
Most gases exist as molecules usually called
DIATOMIC GASES
.
Ex.
, , , , , ,
However, noble gases such as Ne, Ar and He exist as individual atoms. They are called
MONATOMIC GASES
.
Gases have no definite shape and volume.
Gases are easily compressed when pressure is applied.
Gases expand when heated and contract when cooled.
Gases exert pressure.
The densities of gases are relatively small compared to the densities of solids and liquids.
The force of intermolecular attraction between gas particles is negligible.
Gases mix evenly and completely when contained in the same level.
The pressure of the gas is the force exerted by the gas on the walls of its container divided by the surface of the container.
Formula: P= force
area
# greater force on a given area creates a greater pressure.
# greater pressure results when a given force is applied on a small area.
Units
atmosphere = atm
torr = torr
millimeter mercury = mmHg
Instrument BAROMETER
developed by Evangelista Torricelli
Conversion Factor
1 atm = 760 torr = 760 mmHg
1 torr = 1 mmHg
PASCAL = 1 newton = 1 kg
Atmospheric Pressure decreases as the altitude increases
VOLUME
The volume of a gas is equal to the volume of the container since a gas completely fills its container.
Units
m3, cm3, L, mL
TEMPERATURE
The Kelvin temperature is used in all calculations with gases. The following are the useful formulas in connecting one unit of temperature to another.
= 5/9 ( -32)
= 9/5 ( +32)
= +273
Instrument THERMOMETER
discovered by
Daniel Gabriel Fahrenheit and;
Anders Celsius
Formula
mass of gas
molar mass of the gas
n=
DENSITY
Gases are very light. The densities of gases are very small compared with those of solids and liquids.
Formula
mass of gas
volume of gas
D=
Standard Condition
The temperature of a gas and atmospheric pressure vary from place to place and from time to time and since the volume of a gas is dependent on its temperature and pressure, it is important to have a set of standard conditions called STP or Standard Temperature and Pressure.
Volume = 22.4 L
Temperature = 273 K
Pressure = 1 atm = 760 mmHg = 760 torr
Kinetic Molecular Theory
It explains the behavior/properties of gases. This theory is based on several assumptions which explain the measured properties of gases in terms of the behavior of individual gas molecules.
1. Gases are made up of atoms or molecules that continuously move in random and straight line motion.
2. The distance between particles of gases are so wide, compared to other individual sizes. A gas particle is mostly empty space or with negligible volume.
3. The force of attraction between gas molecules is almost negligible.
4. The collision between gas particles and two walls of their container are perfectly elastic. This means that during collision, there is no lose or gain of energy among the particles.
5. The average kinetic energy of a gas is proportional to its temperature in Kelvin.
GAS LAWS
These describe the behavior of gases in terms of their measurable properties.
Boyle's Law
At constant temperature, the volume of a fixed mass of gas is inversely proportional to the pressure exerted on it.
P1 V2
P2 V1
or P1V1 = P2V2
(Pressure and Volume Relationship)
Charles' Law
(Volume and Temperature Relationship)
At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature in Kelvin.
V1 T1
V2 T2
or V1T2 = V2T1
Gay Lussac's Law
(Volume and Pressure Relationship)
At constant volume, the pressure exerted by a given sample of gas is directly proportional to its temperature in Kelvin.
P1 T1
P2 T2
or P1T2 = P2T1
At constant temperature and pressure, the volume of gas is directly proportional to the no. of moles.
n1 V1
n2 V2
or n1V2 = n2V1
Ideal Gas Law
It is the combination of all the gas laws. The most commonly used form of R is 0.821 L
PV = nRT
Combined Gas Law
The volume of gas is directly proportional to the absolute temperature and inversely proportional to the pressure.
P1V1T2 = P2V2T1
Dalton's Law of Partial Pressure
The total pressure exerted by a mixture of gases is the sum of the partial pressure of each individual gas present.

Pt = P1 + P2 + P3 ...
Prepared by Group 1