krit.club logo

States of Matter - Reversible and Irreversible Changes

Grade 3IB

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Matter exists in three primary states: solids, liquids, and gases. A common example is water, which can be found as solid ice, liquid H2OH_2O, and gaseous water vapor.

•

A reversible change is a change that can be undone or reversed. These are usually physical changes where no new substance is formed, such as melting ice into liquid H2OH_2O.

•

An irreversible change is a change that cannot be undone. New substances are created during the process, such as when wood is burned to create ash and smoke.

•

Heating and cooling are the main ways to cause changes in states of matter. Adding heat energy (+ Energy\text{+ Energy}) can cause melting or evaporation, while removing heat (- Energy\text{- Energy}) can cause freezing or condensation.

•

Mixing certain substances can cause irreversible reactions. For example, mixing vinegar and baking soda creates CO2CO_2 gas, which cannot be turned back into the original ingredients easily.

📐Formulae

Solid⇌FreezingMeltingLiquid\text{Solid} \xrightleftharpoons[\text{Freezing}]{\text{Melting}} \text{Liquid}

Liquid⇌CondensationEvaporationGas\text{Liquid} \xrightleftharpoons[\text{Condensation}]{\text{Evaporation}} \text{Gas}

Irreversible Change: A+B→C\text{Irreversible Change: } A + B \rightarrow C

Temperature Change (ΔT)→Change of State\text{Temperature Change (}\Delta T\text{)} \rightarrow \text{Change of State}

💡Examples

Problem 1:

You have a bowl of liquid chocolate. You put it in the fridge for one hour and it becomes solid. Is this a reversible or irreversible change?

Solution:

Reversible change.

Explanation:

The change is caused by cooling. If you add heat to the solid chocolate, it will melt back into a liquid state. No new substance was formed.

Problem 2:

A piece of paper is set on fire and turns into grey ash. Can we turn the ash back into paper?

Solution:

No, this is an irreversible change.

Explanation:

Burning is a chemical process that changes the paper into new substances like ash and smoke (including CO2CO_2). These new substances cannot be combined to recreate the original paper.

Problem 3:

What happens to water (H2OH_2O) when it reaches its boiling point of 100∘C100^{\circ}C?

Solution:

It undergoes evaporation to become a gas (steam).

Explanation:

At 100∘C100^{\circ}C, the liquid H2OH_2O gains enough thermal energy to change its state from a liquid to a gas. This is a reversible physical change.