Lesson 4 of 13
Many become one
Show on a big screenTwo names go in on the left. One name comes out on the right.
Step 1 of 3
- Carbon, on its own. Oxygen, on its own.
- The two groups meet.
- One group of carbon dioxide forms. C + O₂ → CO₂.
Hydrogen is fixed at 4. Slide the oxygen. Read what is left.
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The rule
A combination reaction joins reactants into one product. The balanced equation fixes the exact proportion. Extra reactant waits, unused.
Quicklime is calcium oxide, CaO.
| What runs | The balanced equation |
|---|---|
| Charcoal burns in air | C + O₂ → CO₂ |
| Hydrogen burns in oxygen | 2H₂ + O₂ → 2H₂O |
| Iron meets sulphur on warming | Fe + S → FeS |
| Quicklime meets water | CaO + H₂O → Ca(OH)₂ |
Read each right side. It has one substance, every time.
2H₂ + O₂ → 2H₂O is a recipe. Two portions of hydrogen need one of oxygen.
Many combination reactions give out heat. A reaction that gives out heat is exothermic. Quicklime with water is one. The mixture gets hot enough to feel through the container.
Try the lab to finish this lesson.