Without Doing Any Calculations!

A cylinder contains a mixture of hydrogen and chlorine
molecules. Compare without doing any calculations.

a)the relative mass of the molecules
b)the temperature of each gas
c)the average kinetic energy of the molecules
d)the average speed of the molecules


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Where do you find this

Where do you find this information i.e ave kinetic energy of molecules and temperature of gases or the speed??? I'm taking gr 12 Chem and can't find this info in my textbook or on the net.

a)the relative mass of the

a)the relative mass of the molecules

The average molecular mass (sometimes abbreviated as average mass) is another variation on the use of the term molecular mass. The average molecular mass is the abundance weighted mean (average) of the molecular masses in a sample. This is often closer to what is meant when "molecular mass" and "molar mass" are used synonymously and may have derived from shortening of this term. The average molecular mass and the molar mass of a particular substance in a particular sample are in fact numerically identical and may be interconverted by avogadro's number. It should be noted, however, that the molar mass is almost always a computed figure derived from the standard atomic weights, whereas the average molecular mass, in fields that need the term, is often a measured figure specific to a sample. Therefore, they often vary since one is theoretical and the other is experimental. Specific samples may vary significantly from the expected isotopic composition due to real deviations from earth average isotopic abundances.

b)the temperature of each gas

It is very important to know the temperature history in a spark-ignition engine when the phenomenon of knocking is being studied. However, measurement of the gas temperature is not easy and some work has been done using laser diagnostics etc. In this study, the temperature history until the time of occurrence of knocking in a spark-ignition engine was measured by a form of laser interferometry designed especially for use in the combustion chamber. Not only the change in temperature but also the absolute value of the temperature could be determined with this interferometer, by utilizing the change of the gas density on the reference side. This is a non-intrusive measurement and high resolution is expected. The temperature resolution is about 5 K near the occurrence of knocking.

c)the average kinetic energy of the molecules

To understand a gas and it's properties, we need to lay out a few concepts. In the kinetic molecular theory, there are several postulates upon which we base our explanations.
a gas is composed of molecules that are far apart from each other in comparison to their own dimensions (most volume occupied by a gas is empty space).
gas molecules are in constant random motion, each molecule continues to move in a straight line unless it collides with another molecule or with a wall of the container
the molecules exert no force on each other or on the wall unless they collide. These collisions are elastic (the total translational kinetic remains unchanged).
the average kinetic energy of the molecules is proportional to the absolute temperature.

The kinetic energy of a single molecule is

KE = e = 1/2 mv2 where m is the mass of the particle and v is the speed.

Let's consider a single molecule of mass m traveling with speed v in a box where all sides (x,y, and z) have length L. The average time it takes for the molecule to strike a wall, bounce around and return to a wall to strike it again depends on the component of speed perpendicular to the wall and on L...

We can measure this effect quite handily. Heavy molecules move slower than lighter molecules. Thus, if we were to release two different scents into the air at one time, the one coming from the lighter molecule would be smelled (assuming no wind currents) first by an observer as some distance from the two samples. This effect is also seen when we have helium balloons The helium is a light molecule and quickly escapes through the pores in the latex rubber of the balloon. Balloons inflated by breath (with heavier air molecules) stay inflated much longer.

One other consequence of the Kinetic Molecular Theory is the fact that we've not actually been able to measure the speed of any given molecule, just their average speeds. There is an equation called the Maxwell-Boltzman distribution, which predicts the proportion of molecules in a gas sample to have any given speed (or kinetic energy). We can see this in action from the following diagram plotting the fraction of molecules versus the speed of the molecules for a sample of molecules at several temperatures. An Excel spreadsheet has been kindly supplied by Prof. Horton that allows you to experiment with these settings.

d)the average speed of the molecules

The main difference between water (or any other substance) when it's solid, liquid, or gas is the average speed of the molecules that make up the substance. Molecules are, on the average, moving fastest in a gas such as water vapor, slower in the liquid phase, and slowest in the solid phase, such as water ice. (Related: Water's three phases)

To see how water changes among its phases, let's begin by imagining you could not only see the molecules of water in a glass of water and the air above it, but also measure their speeds.

You'd see the molecules of water moving at a wide range of speeds. Some would be going slowly enough to, for an instant, maybe join with a few other molecules to begin forming a crystal of ice. But the surrounding, faster-moving molecules would hit the slow moving ones, sending them on their ways.

You would also see some molecules zipping along fast enough to fly into the air above the glass - such molecules have evaporated to become water vapor. At the same time, you'd see some water vapor molecules in the air above the glass going slower than most of the molecules of water, nitrogen, oxygen and other gasses in the air. When one of these hits the water in the glass it stays there - this water vapor molecule has condensed into liquid water.

Cool the glass and the average speed of the water molecules in it slows down. When the temperature falls below 32 degrees F (0 Celsius), more and more water molecules are going slow enough to lock together into ice crystals.

Heat the class and the average speed of the water molecules in it speeds up. More and more of them evaporate into the air as water vapor.

If you cool the air above the glass, the average speed of it's molecules slows down and more and more of them are going slow enough to condense into the glass of water.

That's the basics of evaporation and condensation. You can see that condensation has nothing to do with cooler air "holding" less water vapor than warmer air.

The detailed science, of course, gets much more complicated. For instance, water's changes of state add or take up heat, and this latent heat is an important source of energy to drive the weather (Related: Latent heat supplies weather energy)

More on why saying warm air 'holds' more water vapor is wrong

You often hear that condensation begins as the air cools because "cold air can hold less water than warm air." This isn't true. The air does not hold water in the way a sponge holds water - some teachers have been known to use this analogy. Air does not "hold" water the way liquid water holds salt. Scientists have known this since the 19th century, which means anyone book or teacher who tries to tell you that "warm air can hold more water vapor than cold air" is not only wrong, but is also way, way behind the times.

The best Web discussion of all of that that we've found is the "Bad Clouds" part of the Bad Meteorology Web site maintained by Alistair B. Fraser, a professor at Penn State University. He discusses what's wrong with the idea, answers questions you still might have in an FAQ and a link to a history of the idea of air "holding" water vapor. (Related: Alistair B. Fraser: Bad Clouds)

Submited by : Caballos

relative mass

H - 1amu or H2 - 2 amu
Cl - 35.5amu or Cl2 - 71 amu

Chlorine atoms are MUCH larger and more massive.

knowing this, when hydrogen molecules slam into clorine molecules, it would be the same as a freight train (Cl) slamming into a Geo Metro (H).

In other words, I bet the Hydrogen molecules travel much faster as they collide around the space since it takes much less energy to put them into motion.

If the hydrogen is traveling faster - we can relate the velocity to the kinetic energy. So even though the hyrdrogen isn't as massive, the velocity term is squared so it has a greater impact on the energy.
E= 1/2(Mass)x(Velocity)^2

The temperature of a gas is actually related to the kinetic energy......more kinetic energy - higher temperature.

Or you can look it up in a book....


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