Chemical Reactions and Conservation of Matter
How Reactions Work
Reactants to products
In a chemical reaction, atoms are rearranged into new substances. Bonds break and new bonds form, but the atoms themselves are conserved. This is why balanced equations are essential.
Conservation of matter
In a closed system, the total mass before and after a chemical reaction stays the same, even though the substances may change.
Balancing a chemical equation
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Step 1: Write correct formulas for reactants and products.
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Step 2: Count atoms of each element on both sides.
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Step 3: Add coefficients to balance one element at a time.
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Step 4: Recheck all atom counts.
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Step 5: Reduce coefficients to the simplest whole-number ratio.
Which statement is true about a balanced chemical equation?
Balanced equations conserve atoms, not necessarily the number of molecules.
Correct answer: It has the same number of each type of atom on both sides
Why does oxygen help a fire burn more quickly?
Combustion depends on fuel reacting with oxygen.
Correct answer: Oxygen is a reactant that supports combustion.
Common reaction types
Synthesis
- Two or more substances combine
- Often forms a more complex product
- Example:
Decomposition
- One compound breaks apart
- Often requires energy input
- Example:
In a reaction, a catalyst mainly:
Catalysts provide an easier pathway and are not permanently consumed.
Correct answer: Speeds up the reaction without being consumed
What does the law of conservation of matter mean in chemistry?
Atoms are rearranged rather than eliminated or created.
Correct answer: Matter is not created or destroyed in a closed system.
Signs of chemical change
| Observation | Possible meaning |
|---|---|
| Gas produced | A new substance may be forming |
| Temperature change | Energy is being released or absorbed |
| Color change | Chemical composition may have changed |
| Precipitate forms | An insoluble solid may have appeared |