Energy goes in
Endothermic: “endo” is like “enter”.
Take the flame away
A limestone kiln must be kept hot all the time. If the fire goes out, the limestone stops turning into quicklime.
Why does the reaction stop when the energy stops?
What this lesson covers
The idea
Reactions in which energy is absorbed are endothermic reactions.
Take the flame away
A limestone kiln must be kept hot all the time. If the fire goes out, the limestone stops turning into quicklime.
Why does the reaction stop when the energy stops?
- The reaction keeps taking energy in. No energy, no reaction.
- The reaction gives out energy and it ran out
- Limestone gets tired
In or out?
Sort each reaction by what happens to energy.
Endo = enter
Reactions in which energy is absorbed are endothermic reactions.
- Exothermic | Endothermic
- Energy | Heat released | Energy absorbed
- Examples | Burning, respiration, quicklime + water | Decomposition by heat, light or electricity
- Memory | exo = exit | endo = enter
Notes
Reactions in which energy is absorbed are endothermic reactions.
Check yourself
What does “endothermic” mean?
Which reaction is endothermic?
The decomposition reactions we saw all needed energy (heat, light or electricity). So they are:
- Heat is released with the products. That is exothermic.
- The reaction has no products. Every reaction has products. Endo is about energy absorbed.
- Energy is absorbed in the reaction — correct. Yes! Energy enters.
- Thermal decomposition of limestone — correct. Yes! It needs heat all the time: energy is absorbed.
- Burning of coal. Coal burning gives out heat and light: exothermic.
- Quicklime + water. The beaker gets hot: exothermic.
- Exothermic. Exothermic reactions give energy out. Here energy goes in.
- Endothermic — correct. Yes! Energy absorbed means endothermic.
- Neither. They absorb energy, so they are endothermic.