Chemistry
Energy Changes
Energy moves from a place where there is more to where there is less. Physical and
chemical changes that require heat energy are called endothermic. Energy is quantified
on the reactant side of an equation. Physical and chemical changes that release heat
energy are called exothermic. Energy is quantified on the product side of an equation.
Materials:
NH4Cl, CaCl2, HCl, NaHCO3, H2O, thermometer, balance, beaker,
Styrofoam cup, 10 and 50 mL graduated cylinders, zip lock bags, spatula,
weighing boats.
Methods:
Part 1
Reaction A
1. Weigh out 2.2 grams of ammonium chloride.
2. Pour the solid into the bottom of the zip lock bag. Tilt the bag so the
solid falls into one corner. Lay the bag flat on the table.
3. Measure 10 mL of water and pour it into the bag so it pools away from
Cold
the solid.
4. Close the zip lock bag and squeeze it to mix both ingredients.
5. Hold the bag in the palm of your hand and record what you feel.
6. Wash the contents of the bag down the drain. Rinse and dry the bag.
Reaction B
7. Weigh out 3.2 grams of calcium chloride.
Warm 8. Repeat steps 2-6 mixing calcium chloride and 10 mL of water.
Reaction C
9. Weigh out 1.1 grams of sodium bicarbonate.
10. Repeat steps 2-6 mixing sodium bicarbonate and 10 mL of 1.0 M
Hot!
hydrochloric acid instead of water.
Methods:
Part 2
90 Degrees
1. Place an empty, dry Styrofoam cup in a beaker so the cup will not tip.
2. Weigh out 3 times the quantity of the ingredients from one of the above
reactions. These will be assigned in class.
3. Pour the liquid only into the cup. Place a thermometer in the cup so the
bulb is covered by the liquid. Wait a minute for the thermometer to
acclimate to the liquid temperature. Record this temperature.
4. Add the solid to the cup and immediately start recording the
temperature every 10 seconds for 240 seconds.
Conclusions: Use the data from Part 2 to prepare a graph of time vs. temperature.
For each reaction A, B, and C write a chemical equation for what occurred placing the
term HEAT on the appropriate side of the equation. State whether each is a physical
or chemical change and whether each is endothermic or exothermic.
Temperature measures heat energy content. Compare your graph to others in the class.
What happens to heat energy content in endothermic and exothermic reactions?