I would like to see more examples of chemical change

<h2>Chemical Changes in Matter</h2>
<p>When a <strong>chemical change</strong> takes place, new substances are formed in a chemical reaction. These new products may have very different properties from the substances that were there at the start of the reaction.</p>
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<h3>Definition: Chemical change</h3>
<div class="ns-school-defn">
<p>The formation of new substances in a chemical reaction. One type of matter is changed into something different.</p>
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<p>We will consider two examples of chemical change: the decomposition (breaking down) of hydrogen peroxide and the synthesis (forming) of water.</p>
<section>
<h3 class="title">Decomposition of hydrogen peroxide</h3>
<p>The decomposition (breakdown) of hydrogen peroxide (\(\text{H}_{2}\text{O}_{2}\)) to form water (\(\text{H}_{2}\text{O}\)) and oxygen gas (\(\text{O}_{2}\)) is an example of chemical change. A simplified diagram of this reaction is shown in the figure below. The chemical bonds between \(\text{O}\) and \(\text{H}\) in \(\text{H}_{2}\text{O}_{2}\) are broken and new bonds between \(\text{H}\) and \(\text{O}\) (to form \(\text{H}_{2}\text{O}\)) and between \(\text{O}\) and \(\text{O}\) (to form \(\text{O}_{2}\)) are formed. A chemical change has taken place.</p>
<div class="wp-caption alignnone" style="width: 896px"><img alt="409fab022a7f3a0fcf78eff73db62b50.png" height="181" src="https://data.ulearngo.com/assets/df8879db-48a8-4613-bea6-c32b7a1f9ded" width="896"/><p class="wp-caption-text">The decomposition of \(\text{H}_{2}\text{O}_{2}\) to form \(\text{H}_{2}\text{O}\) and \(\text{O}_{2}\)</p></div>
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<h2>Optional Experiment: The decomposition of hydrogen peroxide</h2>
<div class="ns-school-defn">
<section class="activity">
<h3>Aim</h3>
<p>To observe the decomposition of hydrogen peroxide when it is heated.</p>
</section>
<section class="activity">
<h3>Apparatus</h3>
<p>Dilute hydrogen peroxide (about \(\text{3}\%\)); manganese dioxide; <a data-lesson="reaction-rates-in-analysis-test-strips-for-urinalysis" data-subject="chemistry" data-tutorial="chemical-kinetics" href="https://app.ulearngo.com/chemistry/chemical-kinetics/reaction-rates-in-analysis-test-strips-for-urinalysis">test</a> tubes; a water bowl; stopper and delivery tube, Bunsen burner</p>
<img alt="285708b31d13c039b0afd3f14745a8d8.png" src="https://data.ulearngo.com/assets/0e435eba-5177-49b7-baa7-51a866a9f72a"/>
<div class="ns-school-defn2 orange">
<h4>Warning:</h4>
<p>Hydrogen peroxide can cause chemical burns. Work carefully with it.</p>
</div>
</section>
<section class="activity">
<h3>Method</h3>
<ol>
<li>
<p>Put a small amount (about \(\text{5}\) \(\text{mL}\)) of hydrogen peroxide in a test tube.</p>
</li>
<li>
<p>Set up the apparatus as shown above.</p>
</li>
<li>
<p>Very carefully add a small amount (about \(\text{0.5}\) \(\text{g}\)) of manganese dioxide to the <a data-lesson="investigating-elements-and-compounds" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/investigating-elements-and-compounds">test tube</a> containing hydrogen peroxide.</p>
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</ol>
</section>
<section class="activity">
<h3>Results</h3>
<p>You should observe a gas bubbling up into the second test tube. This reaction happens quite rapidly.</p>
</section>
<section class="activity">
<h3>Conclusions</h3>
<p>When hydrogen peroxide is added to manganese dioxide it decomposes to form oxygen and water. The chemical decomposition reaction that takes place can be written as follows:</p>

\[2\text{H}_{2}\text{O}_{2}\text{(aq)} \rightarrow 2\text{H}_{2}\text{O (l)} + \text{O}_{2}\text{(g)}\]

<p>Note that the manganese dioxide is a catalyst and does not take part in the reaction, so we do not show it in the balanced equation. (A catalyst helps speed up a chemical reaction.)</p>
</section>
</div>
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<div class="ns-school-defn2">
<h3>Fact:</h3>
<p>This experiment used the downward displacement of water to collect a gas. This is a very common way to collect a gas in chemistry. The oxygen that is evolved in this reaction moves along the delivery tube and then collects in the top of the test tube. It does this because it is less dense than water and does not dissolve in water, so the water is displaced downwards.</p>
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<div class="ns-school-defn2">
<h3>Did You Know?</h3>
<p>This reaction is often performed without collecting the oxygen gas and is commonly known as the elephant's toothpaste reaction.</p>
</div>
<p>The above experiment can be very vigorous and produce a lot of oxygen very rapidly. For this reason you should use dilute hydrogen peroxide and only a small amount of manganese dioxide.</p>
</section>
<section>
<h3 class="title">The synthesis of water</h3>
<p>The synthesis (forming) of water (\(\text{H}_{2}\text{O}\)) from hydrogen gas (\(\text{H}_{2}\)) and oxygen gas (\(\text{O}_{2}\)) is another example of chemical change. A simplified diagram of this reaction is shown in the figure below. The chemical bonds between \(\text{O}\) in \(\text{O}_{2}\) and between \(\text{H}\) in \(\text{H}_{2}\) are broken and new bonds between \(\text{H}\) and \(\text{O}\) (to form \(\text{H}_{2}\text{O}\)) are formed. A chemical change has taken place.</p>
<div class="wp-caption alignnone" style="width: 742px"><img alt="719dd6c1e28479bbca0a0c50af9ce3f6.png" height="158" src="https://data.ulearngo.com/assets/c07c4103-5aaf-41d1-b1fe-d2eedbe24f13" width="742"/><p class="wp-caption-text">The synthesis of \(\text{H}_{2}\text{O}\) from \(\text{H}_{2}\) and \(\text{O}_{2}\)</p></div>
<h3>Optional Video: Hydrogen Explosion</h3>
<div class="note visit"><iframe allowfullscreen="allowfullscreen" frameborder="0" height="360" src="https://www.youtube.com/embed/ptiCFq5YK3Q?rel=0&amp;modestbranding=1&amp;cc_lang_pref=en&amp;cc_load_policy=1" width="640"></iframe></div>
<div class="ns-school-emp">
<h2>Optional Experiment: The synthesis of water</h2>
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<section class="activity">
<h3>Aim</h3>
<p>To observe the synthesis of water.</p>
</section>
<section class="activity">
<h3>Apparatus</h3>
<p>Hydrogen gas; balloon; string; candle; long stick: ear plugs; safety glasses</p>
</section>
<section class="activity">
<h3>Method</h3>
<ol>
<li>
<p>Half fill a balloon with hydrogen gas.</p>
</li>
<li>
<p>Fill the remainder of the balloon with oxygen gas. (You can also just use your breath to fill the balloon.)</p>
</li>
<li>
<p>Tie the balloon to one end of the string. Tie down the other end of the string so that the balloon is positioned in mid air, away from any people, objects, walls, ceilings etc.</p>
</li>
<li>
<p>Attach the candle tightly to the stick and light the candle.</p>
</li>
<li>
<p>Standing away from the balloon, carefully hold the candle to the balloon.</p>
</li>
</ol>
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<h4>Warning:</h4>
<p>This reaction can be highly explosive, for this reason it is best done outdoors. Always ensure that you wear ear protection or block your ears. Always have more oxygen than hydrogen in the balloon.</p>
</div>
</section>
<section class="activity">
<h3>Results</h3>
<p>When you bring the candle close to the balloon you should see a <a data-lesson="importance-of-understanding-configuration" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/importance-of-understanding-configuration">flame</a> and hear a loud bang.</p>
</section>
<section class="activity">
<h3>Conclusions</h3>
<p>When a <a data-lesson="mixtures" data-subject="chemistry" data-tutorial="classification-of-matter" href="https://app.ulearngo.com/chemistry/classification-of-matter/mixtures">mixture</a> of hydrogen and oxygen gas is set alight with a candle a chemical change occurs. Water is made according to the following equation:</p>

\[2\text{H}_{2}\text{(g)} + \text{O}_{2}\text{(g)} \rightarrow 2\text{H}_{2}\text{O (l)}\]</section>
</div>
</div>
<div class="ns-school-defn2">
<h3>Did You Know?</h3>
<p>A mixture of hydrogen and oxygen gas is used as a <a data-lesson="fuel-cells" data-subject="chemistry" data-tutorial="electrochemistry" href="https://app.ulearngo.com/chemistry/electrochemistry/fuel-cells">fuel</a> to get rockets into space.</p>
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<p>There are some important things to remember about chemical changes:</p>
<ol>
<li>
<p><em>Arrangement of particles</em></p>
<p>During a chemical change, the particles themselves are changed in some way. In the example of hydrogen peroxide that was used earlier, the \(\text{H}_{2}\text{O}_{2}\) molecules were split up into their component atoms. The number of particles will change because each \(\text{H}_{2}\text{O}_{2}\) molecule breaks down into two water molecules (\(\text{H}_{2}\text{O}\)) and one oxygen molecule (\(\text{O}_{2}\)).</p>
</li>
<li>
<p><em>Energy changes</em></p>
<p>The <a data-lesson="energy" data-subject="chemistry" data-tutorial="thermochemistry" href="https://app.ulearngo.com/chemistry/thermochemistry/energy">energy</a> changes that take place during a chemical reaction are much greater than those that take place during a <a data-lesson="physical-chemical-properties" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/physical-chemical-properties">physical</a> change in matter. During a chemical reaction, energy is used up in order to break bonds and then energy is released when the new product is formed.</p>
</li>
<li>
<p><em>Reversibility</em></p>
<p>Chemical changes are far more difficult to reverse than physical changes. When hydrogen peroxide decomposes into water and oxygen, it is almost impossible to get back to hydrogen peroxide.</p>
</li>
<li>
<p><em>Mass conservation</em></p>
<p>Mass is conserved during a chemical change, but the number of molecules may change. In the example of the decomposition of hydrogen peroxide, for every two molecules of hydrogen peroxide that decomposes, three molecules are formed (two water and one oxygen).</p>
</li>
</ol>
<p>The table below highlights these concepts for the decomposition of hydrogen peroxide.</p>
<div>
<table summary="                ">
<tbody>
<tr>
<td> </td>
<td colspan="2">
<p>\(2\text{H}_{2}\text{O}_{2} \rightarrow 2\text{H}_{2}\text{O} + \text{O}_{2}\)</p>
</td>
</tr>
<tr>
<td> </td>
<td><img alt="" src="https://data.ulearngo.com/assets/a75c05b0-ae63-4e95-878a-57e65ffd5996"/></td>
<td><img alt="" src="https://data.ulearngo.com/assets/96b46d6b-af56-4bd6-b1fc-c5b6733019d2"/></td>
</tr>
<tr>
<td>
<p><strong>Molecules</strong></p>
</td>
<td>
<p>two molecules</p>
</td>
<td>
<p>three molecules</p>
</td>
</tr>
<tr>
<td>
<p><strong>Energy changes</strong></p>
</td>
<td>
<p>energy taken in when bonds are broken</p>
</td>
<td>
<p>energy given off when bonds are formed</p>
</td>
</tr>
<tr>
<td>
<p><strong>Mass is conserved</strong></p>
</td>
<td>
<p>\(4(\text{1.01}) + 4(\text{16.0}) = \text{68.04}\)</p>
</td>
<td>
<p>\(2(\text{18.02}) + 2(\text{16.0}) = \text{68.04}\)</p>
</td>
</tr>
<tr>
<td>
<p><strong>Atoms are conserved</strong></p>
</td>
<td>
<p>\(\text{4}\) oxygen atoms, \(\text{4}\) hydrogen atoms</p>
</td>
<td>
<p>\(\text{4}\) oxygen atoms, \(\text{4}\) hydrogen atoms</p>
</td>
</tr>
</tbody>
</table>
<div>
<p><em>Table: Important concepts in chemical change</em></p>
</div>
</div>
</section>

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Chemical Changes in Matter

Chemistry generally explores the substances of which matter is composed, the investigation of their properties and reactions, and the use of such reactions to form new substances. 

Chemistry

Discover the different types of changes that matter can undergo and learn about the laws and principles that govern those changes, including the conservation of mass and volume relationships in gases, as well as the correct way of representing and balancing chemical equations.


Chemical Changes in Matter

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