1. Work done by expanding gas
In this lab, we are interested in the relationship between heat energy transfer to a system’s internal energy and work done by the system on its surrounding. Our first experiment is to find the relationship between expansion and compression of a gas and work done by it.
When we compress gas in the syringe, work are done by us. When we push down the plunger, the pressure exerts an action-reaction force back. From W=∫Fdx and P=F/A, we can derive W=∫PdV.
We first attach a syringe to a flask, then we put the beaker into a beaker filled with hot water. We predict that the plunger of the syringe would move upwards. When the temperature increases, the volume increases as well.
If we let the plunger at its initial position, the plunger exerts a force back. When we move our fingers, as we can see, when the temperature raises, the friction less syringes raises up. This is because the increase in temperature of the flask increases the volume since temperature and volume are directly proportional. When temperature increases, they move faster, and pushes the plunger upwards.
When we put the beaker into the iced water, we predict that the friction less syringes will drop. Volume decrease when the temperature increases. From the experiment, we know that when the temperature decreases, the friction less syringes goes down. This is because the decrease in temperature of the flask decreases the volume since temperature and volume are directly proportional. The piston moves up and down because the piston moves away from molecule during the collision when the molecule bounces off piston. The piston moves toward molecule during collision when molecule gains kinetic energy.
2. First Law of Thermodynamic
We studied the first law of thermodynamics. The first law states that the change in internal energy is equal to the heat added minus the work done. This equation is an expression of conservation of energy. An example of work being negligible and heat being present is when we burn things. Only heat is created and work is not. In reverse, an examples of heat being negligible and work being present is compressing a spring.
3. The fire syringe
We then calculate the temperature it needed to start the fire.
In this lab, we want to light the cellulose based cotton using a fire syringe by pushing the gas very fast, which raises the temperature inside very high. If we push it very fast, we consider the compression to be adiabatic (Q=0), which is a progress that does not have heat exchange. From ideal gas law, we know that a decrease in volume should result in an increase in temperature. In this lab, we burn a piece of cotton using the firs syringe, and use a caliper to measure the initial length of air column, final length of air column, and inner radius of the tube. With all the data we get, we can calculate the experimental temperature for burning a cotton. From the book Fahrenheit 451, we know that paper burns at 451 °F. Since the gas is diatomic, we use V1(T1^5/2)= V2(T2^5/2) to find the final temperature.
We assume the initial temperature to be 293.1 K ( 20ºC), we get our final temperature to be 623 K (350ºC), which is higher than the burning point of paper. The reason for a higher final temperature is because we can only approximately measure the volume we push, also, the temperature is not the exact temperature needed to burn the paper. Any temperature higher than 451 ºF can make it burn.
We have uncertainty because we uses our eyes to estimate the measurement about the length it needed to push to burn the cotton. I get a very small uncertainty which do not cover the difference. I get a % difference for 38.1%. This is caused by the inexact reading of the final height.
Conclusion:
In today's class, we learn a series of equations on gas laws. We learn the equation for isothermal, adiabatic process. We learn the root mean square speed for a molecule. We connect the kinetic energy with internal energy. We also learn that the first law states that the change in internal energy is equal to the heat added minus the work done. W
We assume the initial temperature to be 293.1 K ( 20ºC), we get our final temperature to be 623 K (350ºC), which is higher than the burning point of paper. The reason for a higher final temperature is because we can only approximately measure the volume we push, also, the temperature is not the exact temperature needed to burn the paper. Any temperature higher than 451 ºF can make it burn.
We have uncertainty because we uses our eyes to estimate the measurement about the length it needed to push to burn the cotton. I get a very small uncertainty which do not cover the difference. I get a % difference for 38.1%. This is caused by the inexact reading of the final height.
Conclusion:
In today's class, we learn a series of equations on gas laws. We learn the equation for isothermal, adiabatic process. We learn the root mean square speed for a molecule. We connect the kinetic energy with internal energy. We also learn that the first law states that the change in internal energy is equal to the heat added minus the work done. W
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