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No new substances are formed when a material undergoes a reversible change.

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The change can be undone and the material can return to its original state.

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Reversible changes often happen because of changes in temperature.  They happen by adding or removing heat.

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New substances are formed when a material undergoes a chemical reaction.

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Chemical reactions alter the original materials composition.

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The material or substance cannot return to its original state (mostly).

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Irreversible changes often produce heat, light, gas, and other forms of energy.

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Mixing bicarb soda and vinegar creates a chemical reaction that produces gas (carbon dioxide).  Carbon dioxide cannot be returned to its original substances.

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Adding enough heat to an egg will cook it.  Cooking an egg changes how the proteins in the egg are arranged. Once these proteins have been rearranged, they cannot return to their raw form.

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When paper burns it changes the original material. The paper turns into ash and smoke.  Once paper has been burned it cannot be returned to its original state.

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Water boils when heated to a temperature above 100 °C and changes the liquid into steam.  Steam can be cooled and condensed back into its liquid state.

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When ice is heated it melts from a solid int a liquid (water).  Water can be refrozen back into ice.

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The salt and water can be separated into their original materials by evaporating the water away from the salt particles.

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the material looks different, but no new substance is formed

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heating or cooling changes the material from one state to another. no new substances are formed.

heating chocolate turned it from solid chocolate into melted chocolate. when it cools it will become solid chocolate again.

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the materials may make bubbles, light up. get hot, smell different, or change colour.

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a new substance is formed and is different from the original materials.

when iron is exposed to air and water for a long time it forms a new substance, rust.

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Changes in state. Materials move between...

liquid

solid

gas

But remain the same on a chemical level.

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chopping

boiling

melting

freezing

mixing

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burning

cooking

rusting

rotting

mixing two or more materials together

fermenting

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while a physical change can make materials look different, the new pieces, shape or state remain the same on a chemical level.

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a chemical reaction between two or more materials or substances creates a new substance. The new substance is chemically different from the original material.

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bubbles from gas

vapour from gas

odours

change in colour

sounds - fizzing, bubbling, banging, cracking

change in temperature - becomes hot or cold

lights up

precipitation forms (droplets)

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becoming hard

becoming soft

turning to liquid

changing shape

chopped into smaller pieces.