Endothermic vs. Exothermic reactions

November 19, 2008

Endothermic and Exothermic Reactions

Questions:

                1) What is an exothermic reaction?

                2)  What is an endothermic reaction?

                3) Define the term calorie.

Procedures:

1)      Get  two Styrofoam cups for a calorimeter. Place them inside of one another to double their insulating properties.

2)      Using the graduated cylinder, measure out 50 ml of tap water into the newly constructed calorimeter.

3)      Insert a thermometer and leave in the water for at least 2 minutes. Record the temperature of  the water and record in your lab book.

4)      Measure out 5.00 grams of ammonium nitrate on a piece of paper. Be sure to Tare the scale.(that means you must take into account the weight of the paper)

5)      Dump the ammonium nitrate into the calorimeter with the 50 ml of water.

6)      After two minutes reinsert the thermometer and measure the new temperature of the water. Record in lab book.

7)      Repeat procedures 2 through 6 only instead of using ammonium nitrate, measure out 5.00 grams of calcium Chloride.

8)      Dispose of all liquids in the sink.

9)      Clean up after yourselves and wash your hands.

 

Data table:

 

Volume of water

Initial temp

Final temp

Temp difference

Ammonium nitrate

 

 

 

 

Calcium Chloride

 

 

 

 

 

 

Calculations:

1)      Calculate the amount of heat absorbed or released  from the reactions. Volume of water X change in temperature = calories

2)      Calculate what fraction of a mole of reactant you used in each reaction.

3)      Calculate your expected amount of heat by multiplying the fraction of a mole of reactant times the heat of formation of the compound. (The heat of formation of ammonium nitrate is 87.27 kc/mole and for calcium chloride it is 179.6 kcal/mole)

4)      Using this data calculate your percentage error for the two reactions. (% error = actual amt – theoretical amt/theoretical amt. X 100%)

Conclusion:

                Explain your percentage error. What were some sources of error in this lab?

                What did you learn?

                Why did  the water change temperature?

                Problems ?

                Improvements?

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