Thermal Properties of Matter 2/26/2014

Day2 we continued our labs on thermodynamics.  We fired the class off by heating a brass ring with a gas burner and attempted to push the ball through the hole both when the ring is cool and hot.  The result was obvious as we predicted on our white board:

According to lecture notes, "linear thermal expansion indicates to us how the metal (or other solid material) expands when heated." and we witnessed it once more when we heated a dual material-coated iron bar and it curves towards the side with less expand-ability.  Likewise, when we super-cooled the bar, it curved the other way providing that the heated material with the larger coefficient of linear expansion reacts/grows/shrinks more significantly.

This brings us to our first formal lab.  Professor Mason blew steam through the metal rod that is clamped on one end.  As the temperature of the rod rises by the stem, a rotary motion sensor is used to measure how the rod moves.  We used the angular displacement of the rod to calculate the coefficient of thermal expansion:

Poor Ed holding that bowl as Prof Mason forgets about him.

For the first time since 4A, we were forced to propagate uncertainties.  It turns out that our calculations had potential errors and in motion sensors and much more error sources.  We calculated and accounted all the uncertainties in multiple terms and used the differential approach.  Finally, the coefficient of the rod comes close to either lead or aluminum.  We know it's aluminum because it's CHEAP!   Our resulting alpha value is 0.0000293 and the Linear Coefficient of Aluminum is 24 x 10 ^-6.

Next, we dived right into latent heat.  By transferring an amount of heat energy from the Immersion heater to a mixture of half water and half ice, we can determine the amount of fusion heat energy needed to melt a gram of ice.  First, we predicted the temperature versus time graph and it looked like this ideally.  We noticed that there are plateaus and the temperature does not rise until the ice are completely melted...

However, that's nothing like in real life:  FAIL! lol

We then tried to determine the latent heat of fusion for Ice and the Latent heat of vaporization for water based on the fundamental equations:  

Latent Heat Of Vaporization:

Q_v = ± m L_v

Latent Heat Of Fusion:

Q_f = ± m L_f

Basically it's the same equation only that for each substance and for every phase or phase change the Heat Energy exchanged consists of terms involving:

From the change of mass of the water and the measured output from the immersion heater, we then calculated the Latent Heat of water vapor.  However our results were ALL OVER THE PLACE!

Based on the variation of the groups' different value of heat vaporization, we used excel to calculate the standard deviation (with the help of Clayderman) and the value is much larger than 1.  This means the experiment is not within +/- 1 standard deviation and therefore not precise. According to the textbook, the real value of heat vaporization is 2256000 J/kg.  Our major error/uncertainty is that the amount of water evaporated.  It turns out that water has been evaporating all the time before reaching boiling point and we did not account for that.

Break Time.... :)

WE MADE LIVE PLASMA RIGHT OUT OF PHYSIC FACULTIES' MICROWAVE HECK YEEA!!!

Lastly, we jumped into pressure and Prof Mason used a syringe to pump/decrease volume as we attached the other end with a pressure sensor to plot in Logger Pro.

The pressure apparatus

We first predicted the relationship between pressure, temperature, and volume.  Like we predicted, the pressure has an inverse relationship to volume.  As volume goes down, pressure increases vice-versa.  Then we also correctly predicted the linear proportional relationship of pressure and temperature.

Pressure vs. Volume

 Pressure vs. Temperature

When pressure goes up, the speed of a gas’s molecules increases, the gas molecules hit their container more often. The more frequently the gas impacts the container walls, the higher the pressure

The physical meaning of the slope I think is the compress-ability factor of the substance (in our case, air). This might be the deviations from the ideal gas law that we are yet to cover.  If the slope is huge, rise over run (pressure increases drastically over temperature) then the gas is very unstable and might explode if the tank holding it heats up.  The value makes sense because Googling results of this Z value is all in the 0.xx range.

In a nutshell, we accomplished 3 primary experiments today, 

1. Thermal Expansion,
2. Latent Heats,
3. Pressure versus Volume and Pressure versus Temperature.

Have a great weekend!!  xD