9.2+Pressure+in+Gases

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 * Kelvin scale IB MYP Thermal Physics**

WILT: Explain the pressure of a gas in terms of its molecular motion Recall the effects of changes in pressure, volume and temperature of a gas and solve related problems

**What caused a can to collapse?**

 * 1) **Fill the plastic box with cold water.**
 * 2) **Put 15 milliliters (1 tablespoon) of water into the empty soft-drink can.**
 * 3) **Heat the can on the kitchen stove to boil the water. When the water boils, a cloud of condensed vapor will escape from the opening in the can.**
 * 4) **Allow the water to boil for about 30 seconds.**
 * 5) **Using the tongs, grasp the can and quickly invert it and dip it into the water in the pan.**
 * 6) **The can will collapse almost instantaneously.**

When you heat the can, water molecules inside the can become steam as it boils. The vapor from the boiling water pushed air out of the can. Then you put the can upside down and block the mouth of the can that was filled with water vapor. Cooling the can caused the water vapor in the can to __ condense ,__ creating a partial vacuum. The extremely low pressure or the partial vacuum inside the can made it possible for the pressure of the air outside the can to crush it.

A can is crushed when the pressure outside is __ greater __ than the pressure inside, and the pressure difference is greater than the can is able to withstand. You can crush an open aluminum can with your hand. When you squeeze on the can, the pressure outside becomes greater than the pressure inside. Usually, the air pressure inside an open can is the same as the pressure outside. However, in this experiment, the air was driven out of the can and replaced by water vapor. When the water vapor condensed, the pressure inside the can became much less than the air pressure outside. Then the air outside crushed the can.

=**Ideal Gas laws**=

Phet gas properties Boyles law (P - 1/V) For a fixed mass of gas at constant temperature, the pressure is inversely proportional to volume. P ∞ 1/V when T is constant.
 * The ideal gas applets **

Charles law (V - T) For a fixed mass of gas at constant pressure, the volume is directly proportional to the absolute temperature. V ∞ T when p is constant.

Pressure law, Gay - Lussac law (p-T) For a fixed mass of gas at constant volume, the pressure is inversely proportional to the absolute temperature. p ∞ T when V is constant

Pressure - Temperature - Volume relationship of a gas
Pressure vs absolute temperature for a fixed mass of gas(sim) ||= Figure 9.15 ||= Figure 9.18 || The pressure exerted on a container's sides by an ideal gas is proportional to the absolute temperature of the gas at a constant volume. ||= For an ideal gas at constant pressure, the volume is directly proportional to the absolute temperature in kelvins. ||= At constant temperature, the product of an ideal gas's pressure and volume is always constant. || =Ideal Gas Properties=
 * = ===Pressure-Temperature(Pressure law)=== ||= ===Volume-Temperature(Charles law)=== ||= ===Pressure- Volume(Boyles law)=== ||
 * = The pressure of a fixed mass of gas p is directly proportional to its temperature T when its volume is constant. ||= The volume V of the gas increases proportionally with the increase in temperature T. ||= The pressure p is inversely proportional to volume V. ||
 * = Figure 9.12
 * = [[image:http://upload.wikimedia.org/wikipedia/en/math/6/c/6/6c6a35ce4507d81696a7a01125715174.png width="250" height="40" align="center"]]
 * Pressure in gases is due to the __ collision __ of __ molecules __ with the __ walls __ of the container.
 * The pressure of a fixed mass of gas, //p//, is __ directly proportional __ to its __ temperature __ __ //T// __ if its __volume__ is constant.
 * The volume //V// of a fixed mass of a gas __ increases __ proportionally with the increase in __ temperature __ __ //T// __ while __pressure__ remains constant.
 * The pressure of a fixed mass of gas, //p//, is __ inversely proportional __ to the __ volume __ of the gas, __ //V// __, when the __temperature__ __//T//__ is held constant.

Kelvin scale also known as absolute temperature also known as __thermodynamic temperature scale__ (Temperature in a measure of motion of gas particles). Zero kelvin = absolute zero temperature. At this temperature, the particles don't move.

Universal gas law
(p/T)(V/T)(pV) = (k 1 )(k 2 )(k 3 ) pV/T = (k 1)( k 2 )(k 3) = constant p1V1/T1 = p2V2/T2
 * p ∞ T(k) || V ∞T(k) || p ∞ 1/V ||
 * p = k 1 T || V = k 2 T || p = k 2 /V ||
 * p/T= k 1 || V/T = k 2 || pV = k 3 ||

Example) A fixed mass of gas of volume 2.0//litre// expands to 2.5l when its temperature doubles. If the initial pressure is 3.0 x 10 5 Pa, what is the final pressure? Final pressure is 4.8 x 10 5 Pa

pV/T = constant for fixed mass of gas For an amount of gas, n moles [Remind: 6.02 x 10 23 particles] pV/T = nR, R = universal molar gas constant = 8.31 J mol -1 K -1 R = pV/nT => You must use SI units for this but it is true for all gases (if they behave ideally).

pV = nRT, p = pressure in pascals V = volume in m2 n = number of mols R = universal molar gas constant J mol -1 K -1 T = absolute temperature in kelvin


 * Homework**
 * Do practice questions page 166, 167 on your jotter book.**

media type=youtube key=B48XgtYWHug width=560 height=315 width="560" height="315" THE ABSOLUTE ZERO - DOCUMENTARY [|Aerospace Engineering] Published on 28 Jan 2017