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Heat of Reaction

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Purpose

To determine if heat will be released or absorbed during certain acid/base chemical reactions.

Hypothesis

Heat of reaction is the quantity of heat released or absorbed in a chemical reaction. Water (a neutral substance) has a specific heat capacity of one unit. The specific heat capacities of other substances are different but bear a constant ratio to that of water. Therefore, if adding room temperature water to room temperature water results in no measurable amount of heat being released or absorbed, then it is possible that adding different strengths of room temperature acids and bases to room temperature water may react in such a way that a measurable amount of heat may be released or absorbed.

Materials Needed

Note: All materials must be at room temperature
  • 3 beakers (600 ml each)
  • distilled water (1 liter)
  • TI thermometer
  • whole milk (200 ml)
  • household ammonia (200 ml)
  • squeezed lemon juice (200 ml)
  • liquid antacid (200 ml)
  • 100% grapefruit juice (200 ml)
  • baking soda (200 ml)
  • triple beam balance
  • chemistry or physics textbook containing the specific heat capacities for the acids and bases tested

Experiment

Five variables consisting of acid and base combinations—weak acid + strong base, strong acid + weak base, medium acid + medium base, weak acid + weak base, and strong acid + strong base—will be added separately to distilled water (the purpose of which is to provide a constant temperature environment for the acids and bases being tested) and will be tested for the quantity of heat released or absorbed by their combinations.

Procedures

  1. Place 200 ml of distilled water into one beaker (beaker 1), insert the thermometer and stir until a constant temperature is reached, measure the temperature in degrees Celsius and record the temperature (should be at or around room temperature).
  2. The first reaction will be completed with milk and ammonia (weak acid and strong base). Place 100 ml of milk into beaker 2. Place 100 ml of ammonia into beaker #3. Insert the thermometer into the milk and stir until a constant temperature is reached, measure the temperature in degrees Celsius, and record the temperature (should be at or around room temperature). Do the same for beaker 3 containing the ammonia. Then, pour beaker 2 and beaker 3 into beaker 1 at the same time. Insert the thermometer into beaker 1 and stir until the solution is evenly distributed throughout while recording the temperature every 2 seconds for a total period of 20 seconds.
  3. Pour all the liquids out and clean the beakers.
  4. Start the second reaction (strong acid and weak base) with the squeezed lemon juice and liquid antacid. Repeat steps 1 and 2.
  5. Start the third reaction (medium acid and medium base) with the grapefruit juice and baking soda. Repeat steps 1 and 2.
  6. Start the fourth reaction (weak acid and weak base) with the milk and antacid. Repeat steps 1–2.
  7. Start the fifth reaction (strong acid and strong base) with the lemon juice and ammonia. Repeat steps 1–2.
  8. Collect all of your data and organize them in a table.
  9. Calculate the temperature changes in each of the five solutions.
  10. Find the mass in grams using your balance scale for each reaction (2 solutions + water).
  11. Once you have gathered your data from steps 9–10, you can then calculate the total heat released or absorbed during each chemical reaction. The total heat is calculated using this formula:
  12. Total heat = specific heat capacity (J/g °C) × mass (grams) × the difference in temperature (°C)

Note: The specific heat capacity of a substance is the quantity of heat required to increase the temperature of unit mass of the substance by one degree. Specific heat capacity for liquids is a constant that can typically be found in a chemistry or physics textbook.

Results

  1. What was the total heat of each reaction?
  2. Was heat absorbed or released in each reaction?
  3. Does a stronger acid or a stronger base correlate to heat being absorbed or released in the reaction? Does a weaker acid or weaker base correlate to heat being absorbed or released in the reaction?
  4. What practical applications would this experiment have for industry?
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