Chemistry Honors – Classes 42 & 43
- Period B: Wednesday, November 19th and Friday, November 21st (LAB)
- Period D: Thursday, November 20th and Friday, November 21st (LAB)
- Period G: Thursday, November 20th and Monday, November 24th (LAB)
New Unit – Thermochemistry (Textbook Chapter 6)
- Energy changes accompany chemical / physical processes
- dissolving / burning / melting – ANYTHING
- the quantity is part of the process (reactant or product)
- units = joules or calories (convert between them)
Determining Energy of Process
- calorimeter – device that helps us to measure heat flow
- water is the key – it’s easy to measure heat into and out of water
- Q = mCDT (mass, specific heat capacity, change in temp)
- So, why is this useful?
Laboratory Overview – Energy of a Peanut
- empty soda can holds water
- cork to hold the paper clip which supports peanut
- stand that supports holder which grabs thermometer
- burn peanut – changes temp water
- energy into water = energy out of peanut
- Lab Goal – determine the energy content of the peanut
Laboratory Investigation Details
- Materials: ring stand, iron ring, large cork, matches, balance, 200ml beaker, 12-oz. soda can, thermometer, thermometer holder, scissors, tongs, shelled peanut
- Be sure the room is well ventilated. Use gloves or forceps to handle hot equipment and burned peanut.
- Empty the soda can without removing the top tab. Gently bend the tab so that it is vertical. Thread a metal spatula through the tab and balance the can on the iron ring attached to the ring stand and adjust the height accordingly. Remove the can from the ring stand.
- Add about 200ml of water to the soda can, and measure the mass of the water in the can. Reattach the can with the water to the ring stand.
- Place the thermometer into the mouth of the can, suspended from the ring stand in the water (not touching the can). Before going any further, check the apparatus to make sure that everything is secured.
- Straighten part of the paper clip and leave one end bent. Turn the cork upside down and poke the straight end into the cork. The bent or looped end of the clip (it should be flat) is the platform for the peanut.
- Choose a peanut and measure its initial mass using a weigh boat.
- Take an initial temperature reading of the water in the can.
- Place the peanut on its stand. Use a match to set the peanut on fire. This may take several tries. Closely observe the nut as it burns. If the peanut falls off the stand, start over immediately.
- As soon as the peanut stops burning, immediately take a final water temperature reading and record it in the data table.
- As soon as the peanut has cooled, use forceps to lift the burned remains onto a weigh boat on the balance. Measure the final peanut mass and record in the data table.
Lab Calculations to Complete
- Energy absorbed by the water (J)
- Energy released by the peanut (J)
- Mass of peanut consumed (g)
- Energy released per gram of peanut (J/g)
- Energy released per gram of peanut (Cal/g)
- Percent Difference from Known
Known Values – Energy per 28 Grams
- Cashew = 160 Cal
- Macadamia Nut = 210 Cal
- Peanut = 170 Cal