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I CAN investigate and classify chemical reactions based on the evidence of a chemical change.
I CAN investigate and identify evidence of chemical changes, including changes in phase, appearance, colour, odour, and energy.
Bell Ringer
Bell Ringer
Is it a Chemical Reaction?
Students rotate through different stations with small demonstrations (or teacher-led demos):
Dissolving sugar in water
Mixing vinegar and baking soda
Lighting a candle
Crumpling paper
Adding food coloring to water
Students fill in a chart:
Using your senses, describe what happened.
Was it a chemical or physical change? Why?
Discuss as a class.
Mini Lesson
Mini Lesson
I CAN Investigate and Classify Chemical Reactions Based on the Evidence of a Chemical Change
Chemical reactions involve the rearrangement of atoms to form new substances. By observing the changes that happen during a reaction, we can classify the type of chemical reaction and understand what’s happening at the molecular level.
What is a Chemical Change?
A chemical change occurs when a substance undergoes a transformation that produces one or more new substances with different properties. This is different from a physical change, where the substance itself doesn’t change chemically (e.g., melting ice, tearing paper).
Evidence of a Chemical Change:
When a chemical change happens, certain evidence can help us identify it. These clues can include:
Change in Phase:
Solid → Liquid → Gas:
The formation or disappearance of solids, liquids, or gases during a reaction.
Example: When you mix baking soda with vinegar, a gas (carbon dioxide) is produced.
Change in Appearance:
The reactants may change shape or form a new substance with a different appearance.
Example: A metal can tarnish (oxidize) and change colour, like when iron rusts.
Change in Colour:
A chemical reaction can cause the reactants or products to change colour.
Example: When iron rusts, it changes from metallic grey to reddish-brown.
Change in Odour:
A new smell may be produced as a result of a chemical reaction.
Example: When vinegar reacts with baking soda, a sour smell may be produced.
Energy Change:
A chemical reaction can release or absorb energy. This can be in the form of heat, light, or sound.
Exothermic: Reactions that release energy (e.g., burning fuel).
Endothermic: Reactions that absorb energy (e.g., cold packs).
Example: When a match is lit (combustion), energy is released in the form of heat and light.
I CAN Investigate and Identify Evidence of Chemical Changes, Including Changes in Phase, Appearance, Colour, Odour, and Energy
Types of Chemical Reactions:
Types of Chemical Reactions:
Chemical reactions can be classified based on how the atoms are rearranged and the types of substances involved. Below are the main types of chemical reactions you will investigate:
Composition (Synthesis) Reactions
Definition: Two or more simple substances combine to form a more complex compound.
General Formula: A + B → AB
Example: When hydrogen gas reacts with oxygen gas, water is formed: 2H2+O2→2H2
Evidence: You might observe a change in appearance or temperature when the reaction happens.
Decomposition Reactions
Definition: A single compound breaks down into two or more simpler substances.
General Formula: AB → A + B
Example: When hydrogen peroxide decomposes into water and oxygen gas: 2H2O2→2H2O+O2
Evidence: Gas may be produced, or the substance might change colour as the reaction occurs.
Combustion Reactions
Definition: A substance reacts with oxygen to produce heat and light, typically resulting in the formation of carbon dioxide and water.
General Formula: Hydrocarbon + O₂ → CO₂ + H₂O
Example: Burning methane gas: CH4+2O2→CO2+2H2O
Evidence: Heat, light, and sometimes a change in colour (e.g., flames) occur.
Neutralization Reactions
Definition: An acid reacts with a base to form water and a salt.
General Formula: Acid + Base → Salt + Water
Example: When hydrochloric acid reacts with sodium hydroxide: HCl+NaOH→NaCl+H2O
Evidence: A colour change may occur, and energy may be released as heat.
Identifying Evidence in Reactions:
Identifying Evidence in Reactions:
To identify evidence of a chemical change, look for these signs during or after the reaction:
Gas Production:
Bubbles or the release of gas indicates that a chemical reaction has occurred.
Example: The fizzing when baking soda reacts with vinegar.
Colour Change:
A change in colour can signify a chemical reaction.
Example: A piece of copper metal reacts with oxygen to form copper oxide, turning it greenish-black.
Energy Change:
A noticeable temperature change, light, or sound can be evidence of a chemical reaction.
Example: Lighting a match releases heat and light—an exothermic reaction.
Formation of a Precipitate:
A solid that forms from two liquids indicates a chemical change.
Example: Mixing solutions of silver nitrate and sodium chloride results in the formation of a white precipitate of silver chloride.
Exit Activity
Exit Activity
For each of the following chemicals, indicate what a physical and chemical reaction might be.
The first one has been done for you.
Baking Soda
Chemical Change: Reacts with vinegar to produce carbon dioxide gas (acid-base reaction).
Physical Change: Dissolves in water.
Water
Sugar
Milk
Paper
Lemon Juice
Salt
Gasoline
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