Lab 3 Energy Changes in Chemical Reactions PDF

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Lab 3 Energy Changes in Chemical Reactions...

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Jade Boyd

Chem 111 Lab 10/13/16

Energy Changes in Chemical Reactions

During a chemical reaction, bonds are broken and new bonds are formed. Energy is needed to break bonds and reactions that need energy are endothermic reactions. Reactions that release energy are called exothermic reactions. The objective of this experiment is to teach us to be able to determine the heat content of a substance and wether or not there is an endothermic reaction taking place or an exothermic reaction.

Heat of solution We started by observing the energy change that occurs when a solid is dissolved in water.

Solid

Ammonium Nitrate, NH4NO3

Calcium Chloride, CaCl2

Volume of water

100 mL

100 mL

Weight of solid

15g

15.01 g

Initial temperature of the solution

23 degrees celsius

23 degrees celsius

Final temperature of the solution

6 degrees celsius

52 degrees celsius

Change in temperature

17 degrees celsius

29 degrees celsius

Endothermic or Exothermic

Endothermic

Exothermic

Change in temperature per gram of solid

1.13 degrees celsius/ gram NH4NO3

1.932 degrees celsius/ gram CaCl2

The first reaction with Ammonium Nitrate was an endothermic reaction because the solution absorbed energy and had a drop in temperature. The second reaction with Calcium Chloride was an exothermic reaction because it released energy and showed an increase in temperature

Heat of Reaction For the second portion of our experiment, we conducted experiments to determine if the overall heat change in a chemical reaction is endothermic or exothermic. First we mixed Laundry Bleach and Sodium Sulfite. Mixture

Laundry Bleach and Sodium Sulfite

Temperature of Bleach in degrees celsius

23

Temperature of Sodium Sulfite in degrees celsius

23

Temperature of Mixture in degrees celsius

38

Change in temperature

25

This reaction was exothermic because it had an increase in temperature. Then for the next experiment we put 15 drops of water on a wooden block. On top of the block we placed a beaker with 20 g of Barium Hydroxide, Ba(OH)2 and 10 g of Ammonium Thiocyanate, NH4SCN. After 3-4 minutes the beaker was frozen to the block.

Heat of Combustion

This portion was to determine how much heat was produced when a substance burns. We placed a small candle and an index card on a balance and placed a clean cola can with water in it above the candle. Foil was placed on the top of the can to stop heat from escaping and the candle was lit for 2-3 minutes.

Initial

2-3 minutes later

Candle + Index Card Weight

12.725 g

12.654 g

Candle Weight

11.519 g

11.449

Index Card Weight

1.205 g

1.205

Temperature of water

22 C

26 C

Amount of water in can

100 mL

Water + Soda Can weight

109.710 g

Change in Temperature

4

Amount of Candle Burned

.017 g

Calories produced by paraffin

400

heat of combustion in joules

1673.6 Joules

These experiments went well. All of the data is recorded in the tables above. We used to equation for calculating calories and the conversion factor 1.0 calories=4.184 J for calculating joules. We noticed that our results on section 3, Heat of Combustion, were different than our classmates and a reason for this could be that our candle has a very small wick and very little wax around the wick. A solution to this problem would be that everyone had unused new candles for their experiments but this would not be cost effective. Another reason for the large range of results would be the distance from the flame to the can. If students were required to put the can an exact amount of centimeters from the flame this issue could be solved as well. Overall the experiment succeeded in showing us students the difference between an endothermic and an exothermic reaction and the different ways energy/heat is absorbed and released in reactions....