Most of the substances that we use or come across in our daily lives are a result of different chemical reactions. Therefore having knowledge about different chemical reactions are considered essential from the school level. The chapter of class 10 on chemical reactions and equations is therefore essential for helping students in forming a strong foundational base for higher classes. It explains in detail the elementary concepts of a chemical reaction and chemical equation. Students will learn about balancing a chemical equation after going through the solutions. Struggling with this chapter of the class 10 science syllabus? Here are some study notes for you!
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The chapter of class 10 on chemical reactions and equations shows that burning a magnesium strip with oxygen turns it into magnesium oxide. The description of this chemical reaction is in the form of a very long sentence. You can write briefly. The easiest way to do this is to write it as a word equation. The response word equation is above-
Magnesium + Oxygen (Respondent)→ Magnesium Oxide (Product)(1.1)
The substances that cause a chemical change in the reaction (1.1), magnesium, and oxygen are the reaction substances. The new substance is magnesium oxide, which is formed as a product during the reaction.
The word equation indicates that the respondents become products, with an arrow between them. The state of elements before the reaction has been depicted on the left side (LHS) with a sign of plus (+) in between. Likewise, the product depicted on the right (RHS) with a sign of plus (+) in between. The arrow indicates the product and the direction of the reaction.
Writing a Chemical Equation
The chapter of class 10 on chemical reactions and equations shows that there is another short way to represent the chemical equation. Using chemical formulas instead of words can make chemical formulas more concise and useful. Chemical equations represent chemical reactions. If you remember the formulas for magnesium oxide, oxygen, and magnesium, you can write the formula for the word above as
Mg + O2 → MgO (1.2)
The chapter of class 10 on chemical reactions and equations suggests counting and comparing the number of atoms in each of the LHS and RHS components. Is the number of atoms in each element the same on both sides? If so, the equation is balanced. Otherwise, the equations are unbalanced because the mass is not the same on either side of the equation. This chemical equation is the structural chemical equation of the reaction. Formula (1.2) is a structural chemical formula for burning magnesium in the air.
Must Read: Manufacturing Industries Class 10
Balancing a Chemical Equation
The chapter of class 10 on chemical reactions and equations draws our attention to the law of conservation of mass that you learned in class 9. Mass cannot be created or destroyed by chemical reactions and equations. That is, the total mass of the elements present in the chemical reaction product should be equal to the total mass of the elements in the reaction.
The chapter of class 10 on chemical reactions and equations tells us, the number of atoms of each element is the same before and after the chemical reaction. Therefore, the structural chemistry equations must be balanced. It is chemically equivalent. (1.2) is it balanced? Let us get to know the balance of the chemical equation systematically. The expression for activity can be expressed as:
Zinc + Sulphuric Acid → Zinc Sulphur + Hydrogen
The word equation above can be represented by the following chemical equation –
.Zn + H2SO4 → ZnSO4 + H2 (1.3))
Consider the balancing of the chemical equation depicted below
Fe + H2O → Fe3O4 + H2 (1.4)
Step 1: The chapter of class 10 on chemical reactions and equations explains to balance chemical formulas, first draw a box around each formula. Do not change the face of the square while balancing the equation.
Fe + H2O → Fe3O4 + H2 (1.5)
Step 2: List the atomic numbers for the various elements in the unbalanced equation (1.5).The element is the number of atoms. The number of atoms:
Product Reader (RHS) (LHS)
Fe 1 3
ח 2 2
Step 3: It is usually advisable to start the equilibrium with the compound that has the highest number of atoms. It can be reactive or productive. Determine which element has the most atoms for this compound. Use these criteria to select Fe3O4 and its elemental oxygen. There are four oxygen atoms on the right and only one in the LHS. Oxygen atomic balance-
Reactive atoms in products oxygen
(I) Primary 1 (H2O) 4 (Fe3O4)
(2) Balance 1 x 4 4
The chapter of class 10 on chemical reactions and equations makes us aware that you cannot change the formulas of elements and compounds engaged in the reaction to compare the number of atoms. For instance, while balancing oxygen atoms, the “4” parameter can be set to four H2O instead of H2O4 or (H2O). Now the partially balanced equation-
(1.6) Fe + 4 H2O → Fe3O4 + H2 (Partially balanced equation)
Step 4: Choose one of these elements where the iron and H atoms are still unbalanced and continue. Let us balance in a partially balanced equation of hydrogen atoms.
To balance the H atomic number, use RHS with four hydrogen molecules.Reactive atoms in products
(I) Primary 8 (4 H2O) 2 (H2)
(2) Balance 8 2 x 4
The equation is-
(1.7) Fe + 4 H2O → Fe3O4 + 4 H2 (Partially balanced equation)
Step Five: Look at the equation above and select the third unbalanced element. There is only one unbalanced element left. Reactive atoms in products
(1) Initial 1 (in Fe) 3 (in Fe3O4)
(2) Balance 1 x 3 3
To detect Fe, we use three Fe atoms in LHS.
3 Fe + 4 H2O → Fe3O4 + 4H2 (1.8)
Step 6: Finally, to validate the equilibrium equation, count the atoms in each element on either side of the equation.
3Fe + 4H2O → Fe3O4 + 4H2 (1.9) (Balance equation)
The number of atoms on each side of the equation. (1.9) Equal. This equation is now in balance. This method of balancing chemical equations, called the multiplication and experiment method, uses the smallest integer coefficient to perform the equation equilibrium experiment.
Step 7: Symbolic Description of Physical Situations Carefully examine the balanced equation above. (1.9). What does this equation tell us about the physical condition of each reaction and product? This equation has no information about their physical condition.
The chapter of class 10 on chemical reactions and equations explains that, to make the chemical equations more informative, the physical condition of the reactants and products are mentioned along with their chemical formulas. The liquid in the gaseous form including water and solid states of the products and reactants are depicted by the symbols (l), (g), (aq), and (s), respectively. The term aqueous solution (aq) is used when a reactant or product exists as an aqueous solution.
Balancing Redox Reactions
Let us consider this equation and understand the process of balancing a redox equation-
The basic ionic form of the equation is-
Fe2+ + Cr2O72- → Fe3+ + Cr3+
Oxidation half reaction is-
Reduction half reaction is-
Use the reduction half method to balance the equation. Balance the atoms in each half of the reaction except H and O atoms.
Cr2O72- (aq) → 2 Cr3+(aq)
Add water molecules as the reaction is taking place in acidic solution. This is to balance the O atoms and hydrogen ions.
Cr2O72- (aq) + 14 H+(aq) → 2 Cr3+(aq) + 7H2O (I)
Then balance the charges in both half reactions.
Fe2+(aq) → Fe3+(aq) + e–
Cr2O72- (aq) + 14 H+ + 6e– → 2 Cr3+ + 7H2O
6 Fe2+(aq) → 6 Fe3+(aq) + 6e–
Two half of the equations are added to get the overall reaction
6Fe2+(aq) + Cr2O72-(aq) + 14H+(aq) → 6Fe3+(aq) + 2Cr3+(aq) + 7H2O (I)
Types of Chemical Reactions
In the ninth lesson, we learned that atoms of one element do not change into atoms of another element during a chemical reaction. The atoms do not disappear from the mixture or appear elsewhere. In fact, a chemical reaction involves breaking bonds between atoms to form new substances. In chapters three and four you will learn about the types of bonds formed between atoms.
A chemical reaction where two or more substances (compound and elements) combine to form a single product is called a combination reaction.
Example: In this experiment, you will need to take quick lime in a beaker. Thereafter, keep adding water to it slowly. Now touch the beaker. You will find a change in temperature.In this experiment water and calcium oxide will react vigorously to produce slaked lime which will release a large amount of heat.
CaO(s) + H2O —-> Ca(OH)2 + Heat
As depicted water and calcium oxide reacts to produce Calcium Hydroxide. Since this reaction produces a single product called calcium Hydroxide from two or more reactants is known as a combination reaction.
A reaction where a large amount of heat is produced along with the formation of other products is known as an exothermic reaction.
Example: The combustion of natural gas is the most common example.
CH4 + 2O2 —–> CO2 (g) + 2H2O (g)
A reaction where the amount of heat produced along with the formation of other products is absorbed within the reaction, it is known as an endothermic reaction.
Example: Decomposition reactions are Endothermic in nature.
6CO2 + 6H2O + Sunlight → C6H12O6 + 6O2
A chemical reaction where a single reactant is broken down into simpler products is known as a decomposition reaction.
Example: If we heat ferrous sulphate crystals it decomposes to ferric oxide. Water is lost in the reaction and the colour of the crystal changes.
This is a type of chemical reaction in which one element is displaced by another during the reaction.
Example: A common example is the reaction of iron with copper sulphate solution.
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Double Displacement Reaction
This is a type of chemical reaction in which the reactants undergo an exchange of ions during the reaction.
Example: An example is a reaction between sodium sulphate and barium chloride.
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
Oxidation is when an element gains oxygen during a reaction, while reduction is when an element loses oxygen. When these two processes happen simultaneously in a reaction, then those are known as redox reactions.
Example: An example of this could be the reaction between zinc oxide and carbon on the application of heat.
ZnO + C → Zn + CO
Check Out: Periodic Classification Of Elements
Hope you found this chapter of class 10 on chemical reactions and equations informative and helpful. In this chapter you have learnt that a complete chemical equation is exhibited through the symbolic representation of reactants, products, and physical states. Are you confused about which stream to choose after 10th to pursue your dream career? Reach out to our experts at Leverage Edu for the best guidance. Sign up for a free counselling session today!