In an endothermic reaction, heat is absorbed from the environment and used in the reaction. In an exothermic reaction, heat is produced by the reaction. We're going to use a temperature sensor to test some reactions to find out if they're endothermic or exothermic.

There are also endothermic and exothermic processes that aren't chemical reactions. One example is an ice cube melting. When it melts, the water undergoes a state change from a solid to a liquid and absorbs heat from the environment. But because it's always just water there's no chemical change.

In the next section you'll use the temperature sensor to read the temperature in the palm of your hand and in a container of ice water. Connect a temperature sensor to digital pin 2 on your Arduino, and connect your Arduino to the computer.

In the following sections we'll use the temperature sensor to gather some data during a reaction. Below you'll see an empty plot, the current reading from the sensor, and controls for recording data. Using a cup of ice water, and the heat from your hand, record a few plots of changing temperature over time.

Start Recording will start plotting data from the sensor. Stop Recording will stop the data collection. While it's stopped you can zoom in or out on the plot using the buttons on the top right, then drag the plot around to see different parts. Clear Data will clear the plot so you can record a new run.

When you're familiar with how to use the temperature sensor, you can move to the next section.

First, gather the following materials:

• Baking soda
• Citric acid powder
• 500 mL beaker
• Distilled water

Next, read through the following procedure. Then, follow the procedure to perform the experiment. If your lab has sinks, perform the experiment near them as the reaction can bubble over the sides of the beaker. If you don't have sinks available, make sure to have towels close at hand.

Important Make sure you're wearing gloves, splash-proof goggles, and lab aprons.

Procedure:

• Add 15 grams of citric acid powder to a clean, dry, 500 mL beaker.
• Add distilled water until there is 50 mL of citric acid solution.
• Stir the solution.
• Place the temperature sensor in the solution.
• Set aside 10 grams of baking soda.
• Once the temperature has stabilized in the citric acid solution, click Start Recording.
• Add the baking soda to the solution and stir it gently. (You can use the temperature sensor to swirl it around).
• Watch the temperature.
• Click Stop Recording when the temperature stops dropping.

If the solution starts to bubble over, you may need to pour some of it off into the sink, or soak it up with a towel. (Citric acid and baking soda are safe to pour down the drain.)

First, gather the following materials:

• Steel wool
• Vinegar
• 500 mL beaker
• 250 mL beaker
• Quarter of a sheet of thick paper or file folder

Next, read through the following procedure. Then, follow the procedure to perform the experiment.

Important Make sure you're wearing gloves, splash-proof goggles, and lab aprons.

Procedure:

• Place a pad of steel wool in a clean, dry, 500 mL beaker.
• Add vinegar until the steel wool is saturated.
• After about 1 minute, gently squeeze out the steel wool and place it in the 250 mL beaker.
• Press the temperature sensor into the steel wool and wrap the steel wool around it so the sensor is surrounded by it.
• Cover the beaker with the file folder or paper. This is to keep heat from escaping.
• Click Start Recording.
• Watch the temperature. Since it will take some time to rise, the sensor will only update once per second.
• Click Stop Recording when the temperature stops rising or after 5 minutes (300 seconds).