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An introduction to how energy moves and changes during chemical processes.
Have you ever wondered why a campfire feels warm or why a glow stick shines in the dark without being plugged into a wall? It's because chemicals are hiding a secret supply of energy!
In every chemical reaction, atoms are rearranged to make something new. But atoms don't move for free! Every single reaction involves a change in energy. Think of energy like the 'currency' of the universe. To break old bonds between atoms, you have to 'spend' energy. When new bonds form, energy is often 'earned' back. Even if you can't see it, energy is always moving between the chemicals and their surroundings. We call the starting materials reactants and the finished materials products.
Quick Check
True or False: Some chemical reactions happen without any change in energy at all.
Answer
False. All chemical reactions involve a change in energy.
Since we can't see atoms, how do we know energy is moving? We look for clues! The two most common forms of energy we notice are heat and light. When a reaction releases energy quickly, it might create a bright flash or a steady glow, like a firefly. If it releases energy as heat, the temperature of the surroundings will go up. Sometimes, reactions even absorb heat, making the area around them feel cold!
When you light a candle, a chemical reaction occurs between the wax and oxygen. 1. The reactants are the wax and oxygen (). 2. As they react, they release energy. 3. You see this energy as a bright yellow light. 4. You feel this energy as heat if you put your hand nearby.
Quick Check
What are the two most common forms of energy we can easily observe during a reaction?
Answer
Heat and light.
Chemicals store energy in their bonds, almost like a battery. This is called chemical potential energy. In some reactions, the reactants have more stored energy than the products. When this happens, the 'extra' energy is released into the world as heat or light. In other reactions, the products end up with more stored energy than the reactants started with. In those cases, the reaction had to 'steal' energy from the environment to make it happen.
Have you used a chemical cold pack for an injury? 1. You squeeze the bag to break a seal, mixing two chemicals (the reactants). 2. These chemicals need energy to form new bonds. 3. They pull heat energy from the surroundings (and your skin!). 4. Because the products have more stored energy than the reactants, the pack feels freezing cold to the touch.
Imagine a reaction where the total energy is represented by . If the reactants start with units and the products only have units, the remaining units must be released. This is why explosions or fires feel so intense—they are dumping huge amounts of stored energy very quickly!
Formula:
Which of these is a common sign that energy is being released during a chemical change?
Where do chemicals store their energy?
If a reaction feels cold, it means the products have more stored energy than the reactants started with.
Review Tomorrow
Tomorrow, try to explain to a friend why a campfire stays hot for a long time using the words 'reactants' and 'stored energy'.
Practice Activity
Find three items in your house that use chemical reactions to create heat or light (Hint: Think about the kitchen or emergency kits!).