Thermodynamics

Hey everybody, and unfortunately welcome back from winter break. Today we started class by going over our unit 6 test. Then we took some notes about energy for the rest of the period. If you missed class today then you can get the notes off Moodle.

First we started talking about two forms of energy, kinetic energy, and potential energy. Kinetic energy is produced with motion. Potential energy is stored energy, and it is produced when not in motion. To relate these two, remember that when kinetic energy goes up, potential energy goes down, and vice versa.

Next we talked about temperature and heat. Temperature is the measurement of the kinetic energy of particles, or how fast the particles are moving. Temperature is measured in degrees of celcius, farenheight, or kelvin. Heat is the measure of energy that transfers from an object of high temperature to an object of low temperature. Heat is measured in units of joules, or the stupid american unit of calories, as Liebs tells us. Remember that heat always transfers from high temperature to low temperature. It never transfers the other way around.

To relate temperature and heat we use heat capacity. Heat capacity is different with every object. It is the amount of heat required to raise the temperature of an object by 1 degree celcius. The formula for heat capacity is:

heat supplied (J) / temperature (C) = heat capacity (J/C)

For the homework we need to figure out how much heat is required to raise an object or a substance by a certain temperature. So use these simple formulas to help you out:

heat required = mass x heat capacity x change in temperature
change in temperature= final temperature - initial temperature

Here is a sample problem:
How much energy is required to increase the temperature of 112 g of water from 35 degrees celcius to 80 degrees celcius, if the heat capacity of water is 4.18 J/gC?
Well this pretty easy, all you do is is find the change in temperature by doing 80-35=45. Then you just plug and chug from here.

energy required = (112 g) x (4.18 J/gC) x (45 C).
so the answer is 21067.2 joules

Well that is all for today. The homework tonight is to finish the Heat Calculations Practice worksheet and maybe review a little for the final if you can. The next scribe is Rachel K.