Technology Idea
Endothermic and Exothermic Reactions
Probeware Lab

Background:

There are two types of chemical reactions; endothermic and exothermic.

Exothermic reactions release heat energy during the reaction - because of this, the surroundings gain heat energy and a temperature increase of the surroundings can be recorded.

Endothermic reactions are just the opposite. Endothermic reactions absorb heat energy - because of this, the surroundings lose heat energy to the reaction and a temperature decrease can be recorded.

In short, a chemical reaction that feels "cooler" is called an endothermic reaction. A chemical reaction that feels "warmer" is called an exothermic reaction.

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The Questions:

What temperature changes, if any, are seen in chemical reactions?

Variables:

Identify the type of data you will collect to support your hypothesis and state the manipulated, responding and controlled variables in this investigation.

SAFETY REMINDER: Wear protective equipment while handling chemicals.

Materials:

  • protective eyewear
  • protective apron and gloves
  • temperature sensor and link to computer
  • beaker, 250 mL
  • two Alka-Seltzer® tablets
  • water
  • ammonium nitrate (this can be obtained by cutting open a "instant cold pack" to release the granules - or ordered from chemical supply)
  • 0.5 Molar hydrochloric acid
  • magnesium ribbon

Procedure:

For this activity, a temperature sensor is used to track the temperature during three different reactions.

In your science notebook, write down your prediction about what will happen to the temperature of the reaction solution when you add the following together:

  • hydrochloric acid and magnesium ribbon
  • ammonium nitrate and water
  • alka-seltzer and water

Step 1:

Connect the temperature sensor to your computer - if you are using a USB sensor, your apparatus will look something like this:

Step 2:

Configure the data collection software to collect temperature data over time.

The following is an example DataStudio graph setup:

Hydrochloric acid and magnesium

Step 3:

Pour approximately 50 ml of hydrochloric acid (HCl) into the beaker. Place the temperature sensor into the beaker of acid. Tear off a piece of magnesium ribbon approximately 10 cm long, and ball it up so it can be dropped into the HCl. Start recording data.

Step 4:

Make sure you have protective gloves on to protect from any bubbling or spray. Gently drop the magnesium ribbon into the HCl. Continue recording for about 30 seconds after the magnesium has reacted, then stop.

Step 5:

When you have finished collecting your temperature data, you are ready to analyze it. Re-scale the graph so the data fills the whole window. If possible, print out the resulting graph.

Find the lowest temperature you recorded. (If you are using DataStudio software, click on the “Smart Cursor” button . The cursor becomes a crosshair which you can drag over the graph in order to more easily determine the coordinates at any particular point.) Write down this temperature in your notes.

Find the highest temperature you recorded. Write down this temperature in your notes.

Carefully dispose of the beaker contents as instructed by your teacher.

Water and ammonium nitrate

Step 6:

Pour approximately 100 ml of water into the beaker. Place the Temperature Sensor into the container of water. Start recording data.

Step 7:

While recording, drop a large spoonful of the ammonium nitrate into the water. Swirl the temperature sensor gently in the water as the ammonium nitrate dissolves. Continue recording for about 30 seconds after the ammonium nitrate has dissolved, then stop.

Step 8:

Repeat the graph analysis you performed in step 5. Carefully dispose of the beaker contents as instructed by your teacher.

Alka-seltzer and water

Step 9:

Pour approximately 100 ml of water into the beaker. Place the temperature sensor into the container of water. Start recording data.

Step 10:

While recording, drop in both Alka-Seltzer tablets. Swirl the temperature sensor gently in the water as the tablets dissolve. Continue recording for about 30 seconds after the tablets have dissolved, then stop.

Step 11:

Repeat the graph analysis you performed in step 5. Carefully dispose of the beaker contents as instructed by your teacher.

Forming Conclusions:

Based on the data you have collected, answer the following questions:

1. What temperature changes, if any, are seen in chemical reactions?
2. Describe in words what happened to the temperature of the water during each of the reactions. Were the reactions endothermic or exothermic? Explain.
3. In the case of a temperature increase, where do you think the thermal energy came from? In the case of a temperature decrease, where do you think the thermal energy went?
4. Did your predictions turn out as you expected?

Extending:

  • Consider a graph that records the energy contained in the substances over time. The energy level of the substances would be on the "y" axis, and time would be on the "x" axis.

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