Monday
Monday: Warm Cup, Cold Cup
Rocket slides two clear cups onto the Bench. "Yesterday my fizz test felt cold," he says. "The cup was cold on the outside!"
Raven sets a kitchen thermometer beside the cups. "Cold is a feeling. A reading is data. What do you notice when we measure?"
Rocket pours vinegar, drops in a spoon of baking soda and watches the foam climb. The thermometer needle creeps downward.
"It really did drop," he says. "Where did the warmth go?"
Nova hovers low, her light steady over the foam. "Energy does not vanish," she says. "Ask where it moved, and what it moved into."
Raven writes the two readings in the Bench Log. "Before and after," she says. "This week, every change gets a thermometer."
The system and the surroundings
Chemists split the world into two parts when they study a change. The system is the specific portion of matter being studied, such as the vinegar and baking soda in the cup.
The surroundings are everything else: the cup, the air, the table and you.
During most changes, energy moves between the system and the surroundings. If the system loses some energy, the surroundings gain exactly that much.
This is the law of conservation of energy. In any physical or chemical process, energy is neither created nor destroyed.
Two directions for heat
A change is exothermic if the system releases heat into the surroundings. The surroundings gain heat, so their temperature goes up.
A change is endothermic if the system absorbs heat from the surroundings. The surroundings lose heat, so their temperature goes down.
The thermometer sits in the liquid, and the liquid is part of the surroundings of the reacting particles. A rising reading means exothermic. A falling reading means endothermic.
Both physical changes and chemical changes can be exothermic or endothermic. Ice melting on a counter takes in heat from the room, so melting is endothermic.
| Thermometer reading | Heat moved | Name |
|---|---|---|
| Goes up | From the system into the surroundings | Exothermic |
| Goes down | From the surroundings into the system | Endothermic |
- Read the question.
- Tap your answer.
| Statement | True or false? |
|---|---|
| Energy can be created inside a cup if the reaction is strong enough. | ? |
| An exothermic change makes the surroundings warmer. | ? |
| An endothermic change absorbs heat from the surroundings. | ? |
| Only chemical changes can be endothermic. | ? |
| A falling thermometer reading means the system absorbed heat. | ? |
Now hold the tip in a cup of tap water for one minute. Record both readings in your Bench Log.
Readings are data. Feelings are hints. This week we use both.
A kitchen thermometer that reads in degrees is all they need. A digital one is easiest to read.
The energy facts come from university-hosted chemistry texts on chem.libretexts.org, which you can read yourself.
Good start. Tomorrow you will meet the real cold packs and hand warmers, and learn how each one makes its energy change.