7.1  Kinetic-molecular theory: states that particles in gases, liquids and solids are in constant motion, and that there is no attraction between molecules of gases.

For a gas, the average speed = 1600 km / hour.  Though this is fast, the particles are bouncing around, and changing directions all the time, so they do not have unimpeded paths of travel.

7.2  Kinetic Energy

Kinetic energy: the energy an object has because of its motion.  So. . . anything that moves has kinetic energy.

Heating a gas increases the kinetic energy of the particles.  Temperature is a measure of the average kinetic energy of the particles in a substance.  So at the same temp particles of all substances have the same KE.  Increased T = increased kinetic energy.  Decreased T = decreased kinetic energy.  

Absolute Zero is the point at which particles stop moving, and therefor have no kinetic energy.  Absolute Zero is zero degrees Kelvin, and -273 degrees Celsius.

• Kinetic energy is directly proportional to Kelvin temperature. (That means that if you, for example, increase the Kelvin temp by doubling it, you double the kinetic energy as well).

   

7.3  Pressure

Gas pressure is the result of the collisions of the particles on the walls of the container.

Pressure of a gas is measured in mm Hg.   760 mm Hg = 1 atmosphere .  So, 1 atmosphere is the amount of pressure required to support 760 mm Hg.    

STP (standard temp and pressure) = a temp of 0 degrees Celsius (or 273 K) and a pressure of 1 atm (760 mm Hg).

7.4  Avogadro's Hypothesis: Equal volumes of gases at the same temp and pressure contain equal numbers of particles.  

• At STP, 1 mol of any gas has 6.02 x 10²³ particles, and occupies 22.4 Liters.  The latter is the molar volume of a gas at STP.

7.5  Diffusion: the spread of a gas through space or through another gas.

This formula:    KE = 1/2 mv²   relates kinetic energy (KE) to the mass (m) and velocity (v) of a body.

7.6  Behavior of Gases

• Effect of Adding Gas = adding a gas to a closed container increases pressure.  

• Effect of Removing Gas = decreases pressure in container.

• Effect of changing the size of the container = reducing container size increases pressure; increasing container size reduces pressure.

• Effect of heating or cooling a gas = raising temp of a gas in a closed container increases the pressure, while cooling a gas in closed container decreases pressure.

• Dalton's law of partial pressures: this says that, at a constant volume and temp, the total pressure of a mixture of gases is equal to the sums of the partial pressure of each individual gas in the mixture.

7.7 The Gas Laws

All gases have these three related properties: Volume (V), Pressure (P), and Temperature (T).  T and V are directly proportional and P and V are inversely proportional.  (Remember that T must be the Kelvin temp).

• Memorize the combined gas law.  Boyle's Law and Charles's Law come from this, so if you know the combined gas law you won't need to memorize the other two.  The combined gas law is:

• When T is held constant it can be dropped from the equation.  Likewise, when V is constant (Boyle's Law) or P is constant (Charle's Law) they can be dropped from the equation.

7.8  The Ideal Gas Law

• The combined gas law is modified for the ideal gas law to include n = moles of gas.

• A constant R is obtained from this equation.  R is called the ideal gas constant and = 0.0821 (L x atm) / (K x mol)

  The form then to use for the ideal gas law is:  P x V = n x R x T

7.9  Liquids

• Vaporization: the conversion to a vapor of a liquid at a temp below its boiling point. (Evaporation is the vaporiztion of a liquid in an open container.)

• Vapor is the gas due to a liquid.  Some of the particles at the surface of a liquid will have enough KE to "jump up" as Dr. Hunsley put it, and become gas.  At the same time, some of the gas particles condense and come down back into liquid.

• The pressure associated with vapor = vapor pressure.  Every liquid has a vapor pressure associated with it.

• When T is raised, the KE of the liquid is raised so that more particles can jump up and become gas.  So raising T increases vapor pressure.

  • When T is raised so much that the vapor pressure is equal to the atmospheric pressure, bubbles of gas form in the liquid.  This is the boiling point.

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