At the beginning of the class, we are going to heat a soda can with water filled in. Then we put it into a container filled with cold water upside-down. Before we put it into cold water, we make some assumptions. We predict that the can will be rapidly imploding. We observe the affects of temperature change on the can. When putting inside the cold water, the steam inside the can condenses rapidly, so it creates a partial vacuum in the can, which causes the imploding of the can.
We guess that it will implode. And the result proves our assumption.
Temperature measures the average kinetic energy. When the particle has collision with the can, they transfer the momentum.
We talk about the equation of pressure. P=F/A
We then derive it to:
We talk about the pressure under water. The shape of the object does not affect the result. The only things it matter are that density of the height.
We use the equations to find the weight of the water we blowed. We can use the difference in height to find the pressure. The pressure is dependent on the height the water rose. The density and the value of gravity remains the same and so using Pressure=Force/Area, the formula can be rearranged to find the weight of the column of water.
We know that P (Pressure), V (Volume), T (Temperature) has some relation.
We predict the relationship between pressure and volume to be hyperbola and inverse proportional. (Bayle’s Law)
We connect a syringe to a electronic pressure sensor. We then push it and record the volume and the pressure. We plug in the data into LoggerPro to see whether our prediction is correct.
Since we do the experiment at a small increment at first, and large increment in the end, the graph looks like a line connect with a curve. If we take enough points, it would be hyperbola. Overall, our prediction is correct. Also, P vs. V is not linear.
Then, we make prediction for P vs. T (Charles’ Law II). We predict that the relationship between pressure and temperature is linear and proportional.
We put a 125 mL flask into boiling water to run the experiment. By collecting the data from the pressure sensor and temperature sensor, we get a graph on LoggerPro.
The LoggerPro graph is roughly linear, which proves our prediction. When we do the best fit, we get the equation P=mx+b, which P is the pressure, b is the initial pressure, x be the temperature and m be the pressure change per 1°C.It seems linear.
After that, we make prediction to the relationship between T vs. V (Charles’ Law I). We put a 25 mL flask into a beaker filled with cold water, room temperature water, and hot water; we measure the pressure for different temperature.
When the pressure is constant, volume and temperature are proportional.
From LoggerPro, T vs. P is a linear relationship and proportional.
For y=mx+b, y is temperature, m is temp vs. volume, x is the volume, and b is the initial temp.
We finally get the ideal gas law equation:
PV=nRT, where P is the pressure, V is the volume, n is the number of moles of gas, R is the gas constant, T is the temperature in Kelvin.
4. Balloon Experiment
To apply the ideal gas law, we do an experiment. First, we make a prediction to the balloon. We predict that when the pressure decreases, the volume of the balloon will increase, and when the pressure returns to its original state, the balloon will also return to its original size.
We put a balloon in a closed space, and decrease the pressure. The balloon becomes bigger. When we increase the pressure to the initial pressure, the balloon becomes even smaller. Pressure and volume has inverse relationship.
From the experiment, we see that when pressure decreases, the volume increase; however, when the pressure returns to room pressure, the balloon shrunk smaller than the original size. It is because the number of moles is less than the first step. Some gas molecules escapes.
We do the same thing to marshmallow. We make some assumptions. We predict that decrease pressure will increase the volume, and the marshmallow will be even smaller when the pressure goes back to room pressure.
Before:
After:
Here's the video clip.
From the experiment, we see that when pressure decreases, the volume increase; however, when the pressure returns to room pressure, the marshmallow shrunk smaller than the original size. It is because the number of moles is less than the first step. Some gas molecules escapes.
Conclusion:
In today’s class, we learn the combination of Boyle’s Law, Charles’ Law I and II, and get the ideal gas law PV=nRT. From P=F/A, we derive the pressure of liquid to be P=P0+ρgh. We learn that P vs V is hyperbola and inverse proportional, P vs T is linear and proportional, and T vs V is linear and proportional.
No comments:
Post a Comment