Ah! This is a optimistic topic!!! Very, very, very interesting. Nothing to say!

Interesting topic, and easy to understand.

are you really enjoying the lesson as am doing

Alasiri it is simple, it means 2 molecules of H2 and 1 molecule of  O2. Is it clear?

in the third example H2O-H2 PLUS O2. why H is 4 is not equal to 2

<h2 data-type="title">Balancing Equations</h2>
<p>The chemical equation described in the <a href="https://app.ulearngo.com/lesson/chemical-equations">previous lesson</a> is <span data-type="term">balanced</span>, meaning that equal numbers of atoms for each element involved in the reaction are represented on the reactant and product sides. This is a requirement the equation must satisfy to be consistent with the law of conservation of matter. It may be confirmed by simply summing the numbers of atoms on either <a data-lesson="dissociation-in-water" data-subject="chemistry" data-tutorial="reactions-in-aqueous-solution" href="https://app.ulearngo.com/chemistry/reactions-in-aqueous-solution/dissociation-in-water">side</a> of the arrow and comparing these sums to ensure they are equal.</p>
<p>Note that the number of atoms for a given element is calculated by multiplying the coefficient of any <a data-lesson="representing-molecules" data-subject="chemistry" data-tutorial="chemistry-essential-ideas" href="https://app.ulearngo.com/chemistry/chemistry-essential-ideas/representing-molecules">formula</a> containing that element by the element’s subscript in the formula. If an element appears in more than one formula on a given side of the equation, the number of atoms represented in each must be computed and then added together.</p>
<p>For example, both product <a data-lesson="amphiprotic-species" data-subject="chemistry" data-tutorial="acid-base-equilibria" href="https://app.ulearngo.com/chemistry/acid-base-equilibria/amphiprotic-species">species</a> in the example reaction, CO<sub>2</sub> and H<sub>2</sub>O, contain the element oxygen, and so the number of <a data-lesson="occurrence-preparation-and-compounds-of-oxygen" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/occurrence-preparation-and-compounds-of-oxygen">oxygen</a> atoms on the product side of the equation is:</p>
<h4>\(\left ( 1\mathrm{\;CO_2} \text{ molecule} × \cfrac{2\text{ O atoms}}{\mathrm{CO_2}\text{ molecule}} \right ) \)\(+ \left ( 2\mathrm{\;H_2O} \text{ molecule} × \cfrac{1\text{ O atom}}{\mathrm{H_2O}\text{ molecule}} \right )\)</h4>
<h4>\(= 4\text{ O atoms}\)</h4>
<p>The equation for the reaction between methane and oxygen to yield <a data-lesson="carbon" data-subject="chemistry" data-tutorial="metals-metalloids-nonmetals" href="https://app.ulearngo.com/chemistry/metals-metalloids-nonmetals/carbon">carbon</a> dioxide and water is confirmed to be balanced per this approach, as shown here:</p>
<h4>\(\mathrm{CH_4} + \mathrm{2O_2} \rightarrow \mathrm{CO_2} + \mathrm{2H_2O}\)</h4>
<table class="medium unnumbered" data-label="" id="fs-idp140513680" summary="This is a table with four columns and four rows. The columns are labeled, “Element,” “Reactants,” “Products,” and “Balanced?”. Under the “Element” column are the letters C, H, and O. Under the “Reactants” column are the equations “1 times 1 equals 1,” “4 times 1 equals 4,” and “2 times 2 equals 4.” Under the “Products” column are the equations, “1 times 1 equals 1,” “2 times 2 equals 4,” and “( 1 times 2 ) plus ( 2 times 1 ) equals 4.” Under the “Balanced?” column are, “1 equals 1, yes,” “4 equals 4, yes,” “4 equals 4, yes.”">
<thead>
<tr valign="top">
<th data-align="left" scope="col">
<h3>Element</h3>
</th>
<th data-align="left" scope="col">
<h3>Reactants</h3>
</th>
<th data-align="left" scope="col">
<h3>Products</h3>
</th>
<th data-align="left" scope="col">
<h3>Balanced?</h3>
</th>
</tr>
</thead>
<tbody>
<tr valign="top">
<td data-align="left">C</td>
<td data-align="left">1 × 1 = 1</td>
<td data-align="left">1 × 1 = 1</td>
<td data-align="left">1 = 1, yes</td>
</tr>
<tr valign="top">
<td data-align="left">H</td>
<td data-align="left">4 × 1 = 4</td>
<td data-align="left">2 × 2 = 4</td>
<td data-align="left">4 = 4, yes</td>
</tr>
<tr valign="top">
<td data-align="left">O</td>
<td data-align="left">2 × 2 = 4</td>
<td data-align="left">(1 × 2) + (2 × 1) = 4</td>
<td data-align="left">4 = 4, yes</td>
</tr>
</tbody>
</table>
<p>A balanced chemical equation often may be derived from a qualitative description of some chemical reaction by a fairly simple approach known as <strong>balancing by inspection</strong>. Consider as an example the decomposition of water to yield molecular hydrogen and oxygen. This process is represented qualitatively by an <em data-effect="italics">unbalanced</em> chemical equation:</p>
<h4>\(\mathrm{H_2O} \rightarrow \mathrm{H_2} + \mathrm{O_2} \text{ (unbalanced)}\)</h4>
<p>Comparing the number of H and O atoms on either side of this equation confirms its imbalance:</p>
<table class="medium unnumbered" data-label="" id="fs-idp104786160" summary="This is a table with four columns and three rows. The columns are labeled, “Element,” “Reactants,” “Products,” and “Balanced?”. Under the “Element” column are the letters H and O. Under the “Reactants” column are the equations “1 times 2 equals 2,” and “1 times 1 equals 1.” Under the “Products” column are the equations, “1 times 2 equals 2,” and “1 times 2 equals 2.” Under the “Balanced?” column are, “2 equals 2, yes,” and “1 does not equal 2, no.”">
<thead>
<tr valign="top">
<th data-align="left" scope="col">
<h3>Element</h3>
</th>
<th data-align="left" scope="col">
<h3>Reactants</h3>
</th>
<th data-align="left" scope="col">
<h3>Products</h3>
</th>
<th data-align="left" scope="col">
<h3>Balanced?</h3>
</th>
</tr>
</thead>
<tbody>
<tr valign="top">
<td data-align="left">H</td>
<td data-align="left">1 × 2 = 2</td>
<td data-align="left">1 × 2 = 2</td>
<td data-align="left">2 = 2, yes</td>
</tr>
<tr valign="top">
<td data-align="left">O</td>
<td data-align="left">1 × 1 = 1</td>
<td data-align="left">1 × 2 = 2</td>
<td data-align="left">1 ≠ 2, no</td>
</tr>
</tbody>
</table>
<p>The numbers of H atoms on the reactant and product sides of the equation are equal, but the numbers of O atoms are not. To achieve balance, the <em data-effect="italics">coefficients</em> of the equation may be changed as needed. Keep in mind, of course, that the <em data-effect="italics">formula subscripts</em> define, in part, the identity of the substance, and so these cannot be changed without altering the qualitative meaning of the equation.</p>
<p>For example, <a data-lesson="factors-affecting-the-equilibrium-constant" data-subject="chemistry" data-tutorial="chemical-equilibrium" href="https://app.ulearngo.com/chemistry/chemical-equilibrium/factors-affecting-the-equilibrium-constant">changing</a> the reactant formula from H<sub>2</sub>O to H<sub>2</sub>O<sub>2</sub> would yield balance in the number of atoms, but doing so also changes the reactant’s identity (it’s now hydrogen peroxide and not water). The O atom balance may be achieved by changing the coefficient for H<sub>2</sub>O to 2.</p>
<h4>\(\mathbf{2}\mathrm{H_2O} \rightarrow \mathrm{H_2} + \mathrm{O_2} \text{ (unbalanced)}\)</h4>
<table class="medium unnumbered" data-label="" id="fs-idm15543696" summary="This is a table with four columns and three rows. The columns are labeled, “Element,” “Reactants,” “Products,” and “Balanced?”. Under the “Element” column are the letters H and O. Under the “Reactants” column are the equations “2 times 2 equals 4,” and “2 times 1 equals 2.” The first 2 in the “2 times 2 equals 4” equation is bold. Under the “Products” column are the equations, “1 times 2 equals 2,” and “1 times 2 equals 2.” Under the “Balanced?” column are, “4 does not equal 2, no,” and “2 equals 2, yes.”">
<thead>
<tr valign="top">
<th data-align="left" scope="col">
<h3>Element</h3>
</th>
<th data-align="left" scope="col">
<h3>Reactants</h3>
</th>
<th data-align="left" scope="col">
<h3>Products</h3>
</th>
<th data-align="left" scope="col">
<h3>Balanced?</h3>
</th>
</tr>
</thead>
<tbody>
<tr valign="top">
<td data-align="left">H</td>
<td data-align="left"><strong data-effect="bold">2</strong> ×<strong data-effect="bold"> </strong>2 = 4</td>
<td data-align="left">1 × 2 = 2</td>
<td data-align="left">4 ≠ 2, no</td>
</tr>
<tr valign="top">
<td data-align="left">O</td>
<td data-align="left">2 × 1 = 2</td>
<td data-align="left">1 × 2 = 2</td>
<td data-align="left">2 = 2, yes</td>
</tr>
</tbody>
</table>
<p>The H atom balance was upset by this change, but it is easily reestablished by changing the coefficient for the H<sub>2</sub> product to 2.</p>
<h4>\(\mathrm{2H_2O} \rightarrow \mathbf{2}\mathrm{H_2} + \mathrm{O_2} \text{ (balanced)}\)</h4>
<table class="medium unnumbered" data-label="" id="fs-idp151419504" summary="This is a table with four columns and three rows. The columns are labeled, “Element,” “Reactants,” “Products,” and “Balanced?”. Under the “Element” column are the letters H and O. Under the “Reactants” column are the equations “2 times 2 equals 4,” and “2 times 1 equals 2.” Under the “Products” column are the equations, “2 times 2 equals 2,” and “1 times 2 equals 2.” The first 2 in the “2 times 2 equals 2” equation is bold. Under the “Balanced?” column are, “4 equals 4, yes,” and “2 equals 2, yes.”">
<thead>
<tr valign="top">
<th data-align="left" scope="col">
<h3>Element</h3>
</th>
<th data-align="left" scope="col">
<h3>Reactants</h3>
</th>
<th data-align="left" scope="col">
<h3>Products</h3>
</th>
<th data-align="left" scope="col">
<h3>Balanced?</h3>
</th>
</tr>
</thead>
<tbody>
<tr valign="top">
<td data-align="left">H</td>
<td data-align="left">2 × 2 = 4</td>
<td data-align="left"><strong data-effect="bold">2</strong> ×<strong data-effect="bold"> </strong>2 = 4</td>
<td data-align="left">4 = 4, yes</td>
</tr>
<tr valign="top">
<td data-align="left">O</td>
<td data-align="left">2 × 1 = 2</td>
<td data-align="left">1 × 2 = 2</td>
<td data-align="left">2 = 2, yes</td>
</tr>
</tbody>
</table>
<p>These coefficients yield equal numbers of both H and O atoms on the reactant and product sides, and the balanced equation is, therefore:</p>
<h4>\(\mathrm{2H_2O} \rightarrow \mathrm{2H_2} + \mathrm{O_2}\)</h4>

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Balancing Chemical Equations

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 fundamentals of chemical reactions, from balancing equations to reaction stoichiometry, and explore topics like acid-base and redox reactions in this tutorial, also uncover titration, gravimetric, and combustion analysis in quantitative chemical analysis.


Balancing Chemical Equations

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