Every day you see matter changing around you - ice...
Science2 zobrazenia·Aktualizované Jun 12, 2026·5 stránkyUnderstanding Chemical and Physical Changes
1 / 5
1
of 5
Understanding the Basics
You'll find this topic everywhere in science, so getting these definitions right will make everything else much easier. A physical change happens when something looks different but is still the same substance underneath - like ice melting into water (it's still H₂O). A chemical change creates completely new substances with different properties.
Think of it this way: if you can easily undo the change, it's probably physical. If you can't turn it back to what it was, it's likely chemical.
The key players in chemical changes are reactants (what you start with) and products (what you end up with). Most physical changes are reversible, whilst chemical changes are usually irreversible.
Top Tip: Ask yourself "Is a new substance formed?" - this is the ultimate test for spotting chemical changes.
2
of 5
Spotting the Differences
This comparison table is absolutely essential for your exams - you'll definitely need to know these differences. Physical changes keep the same substance but change its form (like crushing ice or boiling water). Chemical changes create entirely new substances with different properties.
The big giveaway is reversibility. You can easily freeze water back into ice, but you can't turn ash back into wood. Energy changes happen in both types, but chemical reactions often produce much more dramatic energy changes.
Don't worry about the mass though - it's always conserved in both types of changes. The total mass before equals the total mass after, every single time.
Remember: Changes of state (melting, freezing, boiling) are ALWAYS physical changes, no matter how dramatic they look.
3
of 5
Signs of Chemical Reactions
When you're in the lab, these signs will help you spot chemical reactions happening right before your eyes. Look for colour changes (like metal turning rusty), gas production (bubbling or fizzing), or a precipitate forming (when a solid suddenly appears in a clear liquid).
Energy changes are huge clues too. Exothermic reactions give out heat and warm up the container, whilst endothermic reactions absorb heat and cool things down. You might also notice light, sound, or new smells appearing.
Here's the catch though - one sign alone might not be enough. Boiling water produces bubbles, but that's still a physical change. You need to think about whether a genuinely new substance is being created.
Lab Alert: Don't just rely on one sign - look at the whole picture to determine if new substances are actually forming.
4
of 5
Real-World Examples
Let's test your understanding with some everyday scenarios. Dissolving salt in water is physical because no new substances form - you can get your salt back by evaporating the water. The salt and water are still chemically the same.
Frying an egg is definitely chemical. The clear, runny egg white becomes solid and white through heat, and the proteins change permanently. You'll never turn that fried egg back into a raw one!
Rusting happens when iron reacts with oxygen and water to form iron oxide - a completely new substance that's flaky and reddish-brown. Making tea is mostly physical (boiling, dissolving, diffusion), though some tiny chemical processes might occur with the tea compounds.
Exam Strategy: Always explain your reasoning - don't just say "physical" or "chemical", explain why based on whether new substances form.
5
of 5
Key Points for Success
You've got this! The Law of Conservation of Mass applies to everything - mass is never lost or gained, whether it's physical or chemical changes. Remember that dissolving is always physical (the substance is just spread out, not changed), and all changes of state are physical.
For chemical changes, watch for the classic signs: fizzing, colour changes, precipitates, and energy changes. The ultimate question remains: "Is a new substance formed?"
Keep practising with everyday examples around you. Is cooking chemical or physical? What about breaking glass? The more you apply these concepts to real life, the more confident you'll become.
Confidence Boost: Once you master the "new substance" rule, you'll find this topic much easier than it first appears!
Mysleli sme si, že sa už nikdy neopýtaš...
Čo je Knowunity AI companion?
Náš AI Companion je AI nástroj zameraný na študentov, ktorý ponúka viac ako len odpovede. Postavený na miliónoch zdrojov Knowunity poskytuje relevantné informácie, personalizované študijné plány, kvízy a obsah priamo v chate, prispôsobujúc sa tvojej individuálnej ceste učenia.
Kde si môžem stiahnuť aplikáciu Knowunity?
Aplikáciu si môžeš stiahnuť z Google Play Store a Apple App Store.
Je Knowunity naozaj zadarmo?
Presne tak! Užívaj si bezplatný prístup k študijnému obsahu, spájaj sa s ostatnými študentmi a získaj okamžitú pomoc – všetko na dosah ruky.
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Science2 zobrazenia·Aktualizované Jun 12, 2026·5 stránkyUnderstanding Chemical and Physical Changes
Every day you see matter changing around you - ice melting in your drink, bread toasting, or your bike getting rusty. Understanding whether these are physical or chemical changes is crucial for understanding how the world works and will help...
1
of 5
Zaregistruj sa, aby si videl obsah. Je to zadarmo!
- Prístup ku všetkým dokumentom
- Zlepši si známky
- Pridaj sa k miliónom študentov
Understanding the Basics
You'll find this topic everywhere in science, so getting these definitions right will make everything else much easier. A physical change happens when something looks different but is still the same substance underneath - like ice melting into water (it's still H₂O). A chemical change creates completely new substances with different properties.
Think of it this way: if you can easily undo the change, it's probably physical. If you can't turn it back to what it was, it's likely chemical.
The key players in chemical changes are reactants (what you start with) and products (what you end up with). Most physical changes are reversible, whilst chemical changes are usually irreversible.
Top Tip: Ask yourself "Is a new substance formed?" - this is the ultimate test for spotting chemical changes.
2
of 5Zaregistruj sa, aby si videl obsah. Je to zadarmo!
- Prístup ku všetkým dokumentom
- Zlepši si známky
- Pridaj sa k miliónom študentov
Spotting the Differences
This comparison table is absolutely essential for your exams - you'll definitely need to know these differences. Physical changes keep the same substance but change its form (like crushing ice or boiling water). Chemical changes create entirely new substances with different properties.
The big giveaway is reversibility. You can easily freeze water back into ice, but you can't turn ash back into wood. Energy changes happen in both types, but chemical reactions often produce much more dramatic energy changes.
Don't worry about the mass though - it's always conserved in both types of changes. The total mass before equals the total mass after, every single time.
Remember: Changes of state (melting, freezing, boiling) are ALWAYS physical changes, no matter how dramatic they look.
3
of 5Zaregistruj sa, aby si videl obsah. Je to zadarmo!
- Prístup ku všetkým dokumentom
- Zlepši si známky
- Pridaj sa k miliónom študentov
Signs of Chemical Reactions
When you're in the lab, these signs will help you spot chemical reactions happening right before your eyes. Look for colour changes (like metal turning rusty), gas production (bubbling or fizzing), or a precipitate forming (when a solid suddenly appears in a clear liquid).
Energy changes are huge clues too. Exothermic reactions give out heat and warm up the container, whilst endothermic reactions absorb heat and cool things down. You might also notice light, sound, or new smells appearing.
Here's the catch though - one sign alone might not be enough. Boiling water produces bubbles, but that's still a physical change. You need to think about whether a genuinely new substance is being created.
Lab Alert: Don't just rely on one sign - look at the whole picture to determine if new substances are actually forming.
4
of 5Zaregistruj sa, aby si videl obsah. Je to zadarmo!
- Prístup ku všetkým dokumentom
- Zlepši si známky
- Pridaj sa k miliónom študentov
Real-World Examples
Let's test your understanding with some everyday scenarios. Dissolving salt in water is physical because no new substances form - you can get your salt back by evaporating the water. The salt and water are still chemically the same.
Frying an egg is definitely chemical. The clear, runny egg white becomes solid and white through heat, and the proteins change permanently. You'll never turn that fried egg back into a raw one!
Rusting happens when iron reacts with oxygen and water to form iron oxide - a completely new substance that's flaky and reddish-brown. Making tea is mostly physical (boiling, dissolving, diffusion), though some tiny chemical processes might occur with the tea compounds.
Exam Strategy: Always explain your reasoning - don't just say "physical" or "chemical", explain why based on whether new substances form.
5
of 5Zaregistruj sa, aby si videl obsah. Je to zadarmo!
- Prístup ku všetkým dokumentom
- Zlepši si známky
- Pridaj sa k miliónom študentov
Key Points for Success
You've got this! The Law of Conservation of Mass applies to everything - mass is never lost or gained, whether it's physical or chemical changes. Remember that dissolving is always physical (the substance is just spread out, not changed), and all changes of state are physical.
For chemical changes, watch for the classic signs: fizzing, colour changes, precipitates, and energy changes. The ultimate question remains: "Is a new substance formed?"
Keep practising with everyday examples around you. Is cooking chemical or physical? What about breaking glass? The more you apply these concepts to real life, the more confident you'll become.
Confidence Boost: Once you master the "new substance" rule, you'll find this topic much easier than it first appears!
Mysleli sme si, že sa už nikdy neopýtaš...
Čo je Knowunity AI companion?
Náš AI Companion je AI nástroj zameraný na študentov, ktorý ponúka viac ako len odpovede. Postavený na miliónoch zdrojov Knowunity poskytuje relevantné informácie, personalizované študijné plány, kvízy a obsah priamo v chate, prispôsobujúc sa tvojej individuálnej ceste učenia.
Kde si môžem stiahnuť aplikáciu Knowunity?
Aplikáciu si môžeš stiahnuť z Google Play Store a Apple App Store.
Je Knowunity naozaj zadarmo?
Presne tak! Užívaj si bezplatný prístup k študijnému obsahu, spájaj sa s ostatnými študentmi a získaj okamžitú pomoc – všetko na dosah ruky.
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Nenašiel si, čo hľadáš? Preskúmaj iné predmety.
Študenti nás milujú — a ty budeš tiež.
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Appka je veľmi jednoduchá na používanie a má super dizajn. Zatiaľ som našiel všetko, čo som hľadal, a naučil sa veľa z prezentácií! Určite ju použijem na školskú úlohu! A samozrejme mi to aj veľmi pomáha ako inšpirácia.
Stefan SiOS používateľ
Táto appka je naozaj skvelá. Je tu toľko študijných poznámok a pomoci [...]. Môj problémový predmet je napríklad francúzština a appka má toľko možností pomoci. Vďaka tejto appke som si zlepšil francúzštinu. Odporúčal by som ju každému.
Samantha KlichAndroid používateľka
Wow, som naozaj ohromený. Vyskúšal som túto appku, lebo som ju videl mnohokrát inzerovať a bol som úplne ohromený. Táto appka je TÁ POMOC, ktorú chceš do školy a hlavne ponúka toľko vecí, ako cvičenia a faktové listy, ktoré mi osobne VEĽMI pomohli.
AnnaiOS používateľka