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A chemical change, sometimes called a chemical reaction, is one in which a given substance becomes a new substance (or substances) with different properties and different composition.
Antoine Lavoisier
Antoine Lavoisier
Antoine Lavoisier concluded that mass is conserved in chemical reactions. The atoms are recycled and never created or lost.
Antoine Lavoisier is considered the father of modern chemistry.
He discovered that oxygen is needed for combustion. He named Oxygen and Hydrogen.
He discovered that mass always remains the same before and after chemical reactions. Mass in conserved in chemical reactions! This is a law. He even developed the system of naming chemical compounds that we use today.
The burning of leaves, the baking of bread, and the rusting of iron are all chemical changes in which the original substance changes to completely different substances with different physical and chemical properties.
Compounds can only be made or separated by undergoing chemical changes. The original substance cannot be recovered easily.
Signs of a chemical change include:
Signs of a chemical change include:
- Color Change (Ripening bananas, for example)
- Temperature Change (Heat is given off or taken in) 🔥🧊
- Gas Production 😲 (Fizzing, bubbling, etc... But not boiling)
- Precipitate Formation ❄❄❄❄
4 Types of Chemical Reactions
4 Types of Chemical Reactions
Synthesis = Adding
Decomposition = Breaking Apart
Single Replacement = Think of a dancing couple. In a single replacement reaction a new element cuts in. The new guy cuts in, pushing out the former guy.
Double Displacement = Think of two dancing couples. In double displacement, both couples switch dancing partners.
Hydrogen Gas
Hydrogen Gas
Hydrogen gas is highly explosive. Do you remember the Hindenburg? The blimp was full of highly flammable Hydrogen gas. Oxygen gas in the air reacted with the hydrogen gas and created water vapor. The chemical properties of water are very different from the chemical properties of its component gasses.
2H2 + O2 ➡️ 2H2O
2H2 + O2 ➡️ 2H2O
Reactants! Reaction! Products!
Reactants! Reaction! Products!
Water
Water
Water can be decomposed (taken apart) into its basic elements. The chemical equation shows that two water molecules can be broken down into one oxygen gas molecule and 2 hydrogen gas molecules.
2H2O ➡️ O2 + 2H2
2H2O ➡️ O2 + 2H2
Reactants! Reaction! Products!
The following model shows the same thing: two water molecules can be broken down into one oxygen gas molecule and 2 hydrogen gas molecules.
Imagine burning methane gas with oxygen gas. The combustion of methane results in carbon dioxide gas and water vapor being produced. The resulting products are very different from the reactants.
CH4 + 2O2 ➡️ CO2 + 2H2O
CH4 + 2O2 ➡️ CO2 + 2H2O
Reactants! Reaction! Products!
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