Chapter 6Elaine Teto

The gaseous state

• A gas has no fixed volume or shape, but takes both the shape and volume of its container. In addition, a gas is highly compressible, especially in comparison to the other two states of matter.

Physical Parameters1. Temperature:• Temperature is an indicator of the average kinetic energy that a sample of matter (gases in this case) possesses.• Temperature can be recorded in three different forms, Fahrenheit, Celsius, and Kelvin.

• When dealing with the parameter of temperature, in this chapter, one will always use the Kelvin scale, because it is measured from the Absolute Zero of temperature.

• Absolute Zero is the point at which all internal motion of matter ceases. With no internal motion, matter has no kinetic energy and thus no temperature.

• On the Celsius scale, this temperature is -273.15 C. The Kelvin scale (K) is therefore defined from Celsius (C) according to:

k = C+273.15

2. Pressure• Pressure = force/area• The pressure applied

by the entire column of air above a point at sea level (at 25oC) is by definition one atmosphere (atm) of pressure.

• 1 atm = 760 Torr

3. Moles (number of gas particles)• N = mass/molar mass

4. Volume• Volume is measured in liters.

Some helpful conversions, when dealing with volume are as follows:

• 1L = 1000Ml = 1000 cm3

Laws and formulas

• the Ideal Gas Law, which relates the pressure, temperature, and volume of an ideal gas, was derived from Charles’ Law (V1/T1=V2/T2=K2) and Boyle’s Law (P1V1=P2V2=K1). The equation of the Ideal Gas Law is as follows:

• PV=nRT

• The universal gas constant (R) formula is;

• PV=NkT• In the preceding formula, N is

the number of atom of gas present and k is Boltzmann’s constant, which is related to the universal gas constant by;

• R=NAk

• Where NA is

Avogadro’s number.

Example of the ideal gas law:

• If 333mL of an ideal gas at a temperature of 25 degrees Celsius and a pressure of 750 torr has its temperature lowered to -11 degrees Celsius and its pressure lowered to 730mmHg what will its new volume be in milliliters?

• Vf= (nR) Tf /Pf This formula will give us the final volume (Which is what was asked for)

• N=VIPI/TIR This formula will solve for the amount of gas (moles) which is also unknown. After arranging the formulas, one would end up with:

• VF=PITF/PFTI(VI)

• The given information is:• PI= 750 torr• TI= 25 degrees Celsius (25+273) 298K• VI= 333Ml• TF= -11 degrees Celsius (-11+273) 262K• PF= 730mmHg (torr=mmHg)• Solution: (750 Torr) (262 K)/ (730 Torr)

(298 K) x (333mL)• 301mL

Dalton’s Law Of Partial Pressure

• explains that the total pressure of a mixture of gases equals the sum of the pressure that each would exert if it were present alone.

• FORMULA: PT= P1+P2+P3+…

• Furthermore, one can relate the amount of a given gas in a mixture to its partial pressure. This can be achieved through the formula:

• FORMULA: P1 = X1PT

Example of Dalton’s Law of Partial Pressure:

• A sample of hydrogen gas is collected over water at 14.0 C.  The pressure of the resultant mixture is 113.0 kPa.  What is the pressure that is exerted by the dry hydrogen alone?

• Pdrygas = Ptotal – Pwatervapor

• Look up the vapor pressure of water at 14.0 C 1.6 kPa

• The knowns are:

• Ptotal = 113.0 kPa

• Pwater vapor = 1.6 kPa

• Pdry gas = 113.0 kPa - 1.6 kP

• Pdry gas = 111.4 kPa

Kinetic Theory of Gases• Pressure:• pressure can be

measured in kilopascals (kPa), millimeters of mercury (mmHg), or atmospheres (atm).

• the following conversions are very important to remember, for this topic:

Standard Atmospheric Pressure = 101.3 kPa = 760 mm of Hg = 1.0 atm

1 kPa = 7.50 mm of Hg

• Temperature:• in chemistry the units are

measured in Kelvin. The reason for this is the fact that it is possible to have negative numbers on the Celsius scale, and that would cause problems when measuring the volume of a gas at low temperatures.

• C + 273 = K• K - 273 = C

• Standard temperature and pressure is abbreviated as STP.

• The following equation will aid in equating STP:

• STP = 101.3 kPa and 273 K (or any equivalent values, i.e. 1 atm and 0C)

Dynamic Equilibria• Dynamic equilibria is

established when no further change is occurring, however, the reaction is still continuing

• there are reversible reactions, meaning the reaction can go in either direction, depending upon the conditions.

• There are also closed systems, in which no substance is either added or lost. However, although no substances are added or lost, energy can still be transferred in or out.

• The change from left to right in the equation is known as the forward reaction. The change from right to left is the back reaction. If the conditions of the experiment change (by altering the relative chances of the forward and back reactions happening), the composition of the equilibrium mixture will also change.

Water and the Hydrogen Bond

• In a water molecule the electron shell around hydrogen atoms is thin, giving the hydrogen atom a small positive charge.

• the electron shell around oxygen atoms is thick, causing oxygen to carry an extra negative charge.

• These opposite charges attract, although quite weakly. This weak force is called a hydrogen bond.

• Those which cannot form hydrogen bonds are informally known as slippery. The scientific name for this is "hydrophobic" which means "water fearing".

• molecules which stick to water, such as alcohol and sugar, are called "hydrophilic", meaning "water loving".

Conclusion

• one has learned the fundamental and detailed aspects of the gaseous state.

• It is interesting to see the vast differences of the gaseous state, in comparison to the others.