5C+Ideal+gas+molecules

Back to SLG =5C IDEAL GAS MOLECULES= 5.11 understand the significance of Brownian motion BROWNIAN MOTION: The motion in a fluid of microscopic particles such as pollen or dust due to collisions with much smaller fast-moving molecules in the air. The particles which are seen to dance about are the dust particles, not the molecules. [|LINK TO APPLET OF BROWNIAN MOTION]

5.12 recall that molecules in a gas have a random motion and that they exert a force and hence a pressure on the walls of the container KINETIC THEORY OF MATTER: A theory that matter is made of microscopic particles which are in constant random motion and follow simple physical laws. PRESSURE ACCORDING TO THE KINETIC THEORY: The collisions on the sides of the container by huge numbers of tiny particles accounts for the pressure which is measured.

5.13 understand that there is an absolute zero of temperature which is – 273 °C ABSOLUTE ZERO OF TEMPERATURE: The lowest temperature which can be achieved when the particles in a substance have zero kinetic energy and cease all motion. This occurs at –273°C (zero kelvin)

5.14 describe the kelvin scale of temperature and be able to convert between the kelvin and Celsius scales KELVIN SCALE OF TEMPERATURE: A temperature scale starting at absolute zero whose unit is the same size as a degree Celsius. T(K) = T(°C) + 273 T (°C) = T (K) - 273

EXERCISE: Copy and complete the table.
 * = TEMPERATURE/ ºC ||= TEMPERATURE/ K ||=  ||
 * = 0 ||=  ||
 * = 100 ||=  ||
 * =  ||= 73 ||
 * = -73 ||=  ||
 * =  ||= 473 ||
 * = 27 ||=  ||
 * =  ||= 323 ||

5.15 understand that an increase in temperature results in an increase in the speed of gas molecules TEMPERATURE ACCORDING TO KINETIC THEORY: The Kelvin temperature is proportional to the average kinetic energy of the particles in the gas.

5.16 understand that the kelvin temperature of the gas is proportional to the average kinetic energy of its molecules

5.17 describe the qualitative relationship between pressure and kelvin temperature for a gas in a sealed container

PRESSURE LAW: At constant volume, the pressure of a fixed mass of gas is proportional to its absolute temperature.

ACTIVITY: Open the 'Gas Properties' simulation at PHET. Keep the volume constant and pump in some gas particles. Vary the temperature gradually by heating and record the values of p and T. Plot the graph of p vs T in a spreadsheet, add a trendline and verify whether the Pressure Law is observed. Repeat the activity keeping T constant and varying p and V. Plot a graph of p against V and then manipulate the variables to achieve a straight line graph through the origin. [|LINK TO PHET SIMULATION ON GAS PROPERTIES] or you can find it in the Students' shared area files.

5.18 use the relationship between the pressure and kelvin temperature of a fixed mass of gas at constant volume: EXAMPLE 1: The gas in a cylinder is at pressure 250 kPa and cools down from 350 K to 280 K. What is its new pressure? EXAMPLE 2: A can of gas is heated so that its pressure rises from 1 atm to 1.6 atm. If the initial temperature is 7°C, what is the final temperature in °C?

5.19 use the relationship between pressure and volume of a fixed mass of gas at constant temperature EXAMPLE 1: A bubble of volume 2 ml rises to the surface of a lake from a position where its pressure is 1.5 atm. What is its volume at the surface of the lake (where pressure is 1.0 atm)?

EXAMPLE 2: A



ACTIVITY: Use the PHET Gas Properties simulation (link above) to investigate the variation of Volume with Temperature (K) of a fixed mass of gas **at constant pressure.** Draw a labelled straight line graph in a spreadsheet and deduce the correct relationship between V and T.

HOMEWORK QUESTIONS ON IDEAL GASES [|Ideal Gases HW practice questions.doc]