Chemical Equations (LAQs)

Physical Science | 2. Chemical Equations – LAQs:
Welcome to LAQs in Chapter 2: Chemical Equations. This page contains the most Important FAQs for Long Answer Questions in this Chapter. Each answer is provided in simple English, with a Telugu explanation, and formatted according to the exam style. This will support your preparation and help you secure top marks in your exams.

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LAQ-1 : Why should we balance a chemical equation?

Introduction

Balancing chemical equations is an essential exercise in chemistry. This practice adheres to fundamental scientific laws and ensures the accurate representation and execution of chemical reactions. This brief explanation delves into why balancing a chemical equation is vital.

Adherence to the Law of Conservation of Mass:

1. Balancing for Mass Conservation:
   Balancing chemical equations ensures compliance with the law of conservation of mass.
2. Equivalence of Mass:
   This law states that the mass of the reactants in a chemical reaction must equal the mass of the products formed.

Ensuring Atom Equilibrium:

1. Equal Number of Atoms:
   Balancing chemical equations guarantees that the number of atoms for each element is equal on both sides of the equation.
2. Atomic Consistency:
   This equilibrium confirms that no atoms are lost or gained during the chemical reaction, maintaining atomic consistency.

Representation of a Chemical Reaction:

1. Accurate Reaction Depiction:
   A balanced chemical equation accurately represents the chemical reaction.
2. Facilitating Understanding:
   It provides a clear, understandable visual of the reaction, facilitating further study, and exploration.

Summary

In essence, balancing a chemical equation is fundamental for abiding by the law of conservation of mass, ensuring atomic equilibrium, and providing a true representation of the chemical reaction. This practice underscores the importance of atomic and mass consistency in chemical reactions, supporting accurate scientific study and understanding.

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LAQ-2 : Balance the following chemical equations.

i.Zn_(s)+AgNO_3(aq)→Zn(NO₃)_2(aq)+Ag_(s)

ii.Fe₂O_3(s)+C_(s)→Fe_(s)+CO_2(g)

iii.Ag+H₂S+O₂→Ag₂S+H₂O

iv.Cu_(s)+O_2(g)→CuO_(s)

Introduction:
Balancing chemical equations is crucial for understanding the exact ratios of reactants and products in a chemical reaction. This task ensures adherence to the Law of Conservation of Mass, indicating that atoms are neither created nor destroyed in a chemical reaction. Let’s look at the balanced forms of the provided chemical equations.

Balanced Chemical Equations:

1. Reaction between Zinc and Silver Nitrate:
   Zn_(s) + 2AgNO₃(aq) → Zn(NO₃)₂(aq) + 2Ag(s)
2. Reaction between Iron(III) Oxide and Carbon:
   2Fe₂O₃(s) + 3C(s) → 4Fe(s) + 3CO₂(g)
3. Reaction between Silver, Hydrogen Sulfide, and Oxygen:
   4Ag (s) + 2H₂S (g) + O₂(g) → 2Ag₂S(s) + 2H₂O
4. Reaction between Copper and Oxygen:
   2Cu(s) + O₂(g) → 2CuO(s)

Summary

In conclusion, balanced chemical equations are fundamental for understanding the relationships and ratios between reactants and products in a chemical reaction. Properly balanced equations ensure the conservation of mass, reflecting the exact atomic or molecular changes occurring within the reaction. This information is vital for various calculations and analyses in chemistry, reinforcing the importance of this practice in the field.

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LAQ-3 : Write the balanced chemical equation for the following reaction.
Zinc + Silver nitrate → Zinc nitrate + Silver

Introduction

Balancing a chemical equation is a basic skill in chemistry. It ensures that the same amount of matter is present before and after a chemical reaction, abiding by the Law of Conservation of Mass. This step-by-step guide will help understand how to balance the chemical equation for the reaction between Zinc and Silver nitrate.

Balanced Chemical Equation for Zinc + Silver Nitrate:

Step 1: Write the Unbalanced Equation

Write down the chemical formulas of all substances:
$$\text{Zn (s)} + \text{AgNO}_3 (aq) \rightarrow \text{Zn(NO}_3)_2 (aq) + \text{Ag (s)}$$

Step 2: Compare the Number of Elements on Both Sides

1. Initially, Zinc (Zn) and Silver (Ag) are balanced on both sides.
2. Nitrogen (N) is unbalanced with one atom on the Left Hand Side (LHS) and two atoms on the Right Hand Side (RHS).
3. To balance Nitrogen, add a coefficient of 2 to AgNO_3​ on LHS:
   $$\text{Zn (s)} + 2\text{AgNO}_3 (aq) \rightarrow \text{Zn(NO}_3)_2 (aq) + \text{Ag (s)}$$
4. Now, the Silver (Ag) is unbalanced, so add a coefficient of 2 to Ag on RHS to balance it:
   $$\text{Zn (s)} + 2\text{AgNO}_3 (aq) \rightarrow \text{Zn(NO}_3)_2 (aq) + 2\text{Ag (s)}$$

Step 3: Verify the Balanced Equation

1. Check the number of atoms for each element on both sides.
2. Zn:1, Ag:2, N:2, O:6 on both sides.

Step 4: Final Balanced Equation

$$\text{Zn (s)} + 2\text{AgNO}_3 (aq) \rightarrow \text{Zn(NO}_3)_2 (aq) + 2\text{Ag (s)}$$

Summary

Following these steps ensures a balanced chemical equation, fulfilling the Law of Conservation of Mass. Each atom is accounted for, providing an accurate representation of the chemical reaction. Understanding this process is fundamental for further study and calculation in chemistry.

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LAQ-4 : Write the balanced chemical equations for the following reactions:

1.Calcium hydroxide + Carbon dioxide → Calcium carbonate + water

2.Zinc + Silver nitrate → Zinc nitrate + Silver.

3.Aluminium + Copper Chloride → Aluminium chloride + Copper

4.Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Introduction

Understanding the balanced chemical equations is crucial for a detailed comprehension of chemical reactions. Here’s a breakdown of how to balance the given chemical equations:

Calcium Hydroxide + Carbon Dioxide:

1. Unbalanced Equation:
   $$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$$
2. Balancing Process:
   The equation is already balanced in this case. Each side has one calcium, two oxygen, and two hydrogen atoms.
3. Balanced Equation:
   $$\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$$

Zinc + Silver Nitrate:

1. Unbalanced Equation:
   $$\text{Zn} + \text{AgNO}_3 \rightarrow \text{Zn(NO}_3)_2 + \text{Ag}$$
2. Balancing Process:
   Balance the silver atoms by adding a coefficient of 2 before AgNO₃​ and Ag.
3. Balanced Equation:
   $$\text{Zn} + 2\text{AgNO}_3 \rightarrow \text{Zn(NO}_3)_2 + 2\text{Ag}$$

Aluminium + Copper Chloride:

1. Unbalanced Equation:
   $$\text{Al} + \text{CuCl}_2 \rightarrow \text{AlCl}_3 + \text{Cu}$$
2. Balancing Process:
   • Balance the aluminum atoms by adding a coefficient of 2 before Al and AlCl₃​.
   • Balance the copper atoms by adding a coefficient of 3 before CuCl₂​ and Cu.
3. Balanced Equation:
   $$2\text{Al} + 3\text{CuCl}_2 \rightarrow 2\text{AlCl}_3 + 3\text{Cu}$$

Barium Chloride + Potassium Sulphate:

1. Unbalanced Equation:
   $$\text{BaCl}_2 + \text{K}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + \text{KCl}$$
2. Balancing Process:
   Balance the potassium atoms by adding a coefficient of 2 before KCl.
3. Balanced Equation:
   $$\text{BaCl}_2 + \text{K}_2\text{SO}_4 \rightarrow \text{BaSO}_4 + 2\text{KCl}$$

Summary

Correctly balanced chemical equations ensure adherence to the Law of Conservation of Mass, which states that in a chemical reaction, the mass of the reactants must equal the mass of the products. This fundamental concept is vital for all chemical calculations and studies.

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LAQ-5 : How many grams of O₂ is required for combustion of 480 grams of Mg? Find the mass of ‘MgO’ formed in this reaction (Mg = 24u, O = 16u).

Introduction

In a chemical reaction, it’s essential to know how much of each reactant is needed and how much product will be formed. This information can be found using stoichiometry and the balanced chemical equation.

Balanced Chemical Equation for Magnesium Combustion:

The balanced chemical equation for the combustion of magnesium (Mg) is:
$$2Mg + O_2 \rightarrow 2MgO$$
This equation indicates that two moles of magnesium react with one mole of oxygen to produce two moles of magnesium oxide.

Calculating Oxygen Required:

1. Given:
   • Mass of Mg=480 gm
   • Molar mass of Mg=24 gm/mol
   • Molar mass of O₂​=32 gm/mol
2. Calculation:
   • Based on the balanced equation, 48 gm of Mg requires 32 gm of O₂​ for complete combustion.
   • Using ratios, calculate the oxygen needed for the combustion of 480 gm of Mg:
     $$\left( \frac{480 \, \text{gm Mg}}{48 \, \text{gm Mg}} \right) \times 32 \, \text{gm} \, O_2 = 320 \, \text{gm} \, O_2$$
3. Result:
   • 320 gm of O₂​ is required to combust 480 gm of Mg.

Calculating Magnesium Oxide Formed:

1. Given:
   • Mass of Mg=480 gm
   • Molar mass of MgO=40 gm/mol
2. Calculation:
   • Based on the balanced equation, 48 gm of Mg produces 80 gm of MgO.
   • Using ratios, calculate the MgO formed from the combustion of 480 gm of Mg:
     $$\left( \frac{480 \, \text{gm Mg}}{48 \, \text{gm Mg}} \right) \times 80 \, \text{gm} \, MgO = 800 \, \text{gm} \, MgO$$
3. Result:
   • 800 gm of MgO is formed from the combustion of 480 gm of Mg.

Summary

To summarize, for the combustion of 480 gm of Mg, 320 gm of O₂​ is required, and 800 gm of MgO is produced as the product. Understanding these calculations is crucial for various applications, including industrial processes and scientific research.

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LAQ-6 : Balance the following chemical equation after writing the symbolic representation.
Calcium hydroxide (s) + Nitric acid (aq) → Water (I) + Calcium Nitrate (aq)

Introduction

Balancing chemical equations is crucial for understanding the ratios in which substances react and are produced. The given unbalanced equation involves calcium hydroxide reacting with nitric acid to produce water and calcium nitrate. This guide will help in balancing this equation step by step.

Step 1: Write the Unbalanced Equation
To begin, write down the unbalanced equation using the correct chemical formulas for each compound involved in the reaction.

$$\text{Ca(OH)}_2 (s) + \text{HNO}_3 (aq) \rightarrow \text{H}_2\text{O} (l) + \text{Ca(NO}_3)_2 (aq)$$

Step 2: Balance the Atoms of Each Element
Next, count the number of atoms of each element on both the reactant and product sides. Adjust coefficients to balance the equation.

In this case: Balance the hydrogen and oxygen atoms by putting a coefficient of 2 in front of HNO₃​ and H_2​O.

$$\text{Ca(OH)}_2 (s) + 2\text{HNO}_3 (aq) \rightarrow 2\text{H}_2\text{O} (l) + \text{Ca(NO}_3)_2 (aq)$$

Step 3: Ensure Coefficients are in the Smallest Ratio
Check the equation to ensure that the coefficients are in the smallest possible whole number ratio.

In this case: The coefficients are already in the smallest ratio.

Step 4: Verify the Balanced Equation
Finally, verify the balanced equation by recounting the atoms of each element on both sides to ensure they are equal.

$$\text{Ca(OH)}_2 (s) + 2\text{HNO}_3 (aq) \rightarrow 2\text{H}_2\text{O} (l) + \text{Ca(NO}_3)_2 (aq)$$

Summary

Now, the balanced chemical equation is:

$$\text{Ca(OH)}_2 (s) + 2\text{HNO}_3 (aq) \rightarrow 2\text{H}_2\text{O} (l) + \text{Ca(NO}_3)_2 (aq)$$

Every atom is balanced on both sides of the equation, fulfilling the Law of Conservation of Mass.

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LAQ-7 : You have brushed the wall with an aqueous suspension of Ca(OH)₂ After two days the wall turned to white colour. Write the balanced chemical reactions for the above changes using the appropriate symbols and formulae.

Introduction

When a wall is brushed with an aqueous suspension of calcium hydroxide, Ca(OH)₂​, it initially might not appear very white. However, over time, the wall turns white due to a chemical reaction with carbon dioxide in the air, forming calcium carbonate, a white compound.

Chemical Reaction:

The aqueous suspension of calcium hydroxide reacts with carbon dioxide (CO₂) in the air. This chemical reaction results in the formation of calcium carbonate (CaCO₃​), a white solid, and water (H₂O).

Balanced Chemical Equation:

The balanced chemical equation for the reaction is as follows:

$$\text{Ca(OH)}_2 \, (aq) + \text{CO}_2 \, (g) \rightarrow \text{CaCO}_3 \, (s) + \text{H}_2\text{O} \, (l)$$

In this equation:

• Ca(OH)₂ (calcium hydroxide, in aqueous form) and CO_2​ (carbon dioxide gas) are the reactants.
• CaCO₃​ (calcium carbonate solid) and H₂​O (water liquid) are the products.

Explanation of the Whitening Process:

As the water produced in the reaction evaporates, the white calcium carbonate remains on the wall, giving it a white color. The calcium carbonate adheres to the wall surface, providing a durable white coating.

Summary

The whitening of the wall brushed with an aqueous suspension of Ca(OH)₂​ is a result of the reaction between calcium hydroxide and carbon dioxide in the air, producing white calcium carbonate and water. This chemical transformation is represented by the balanced equation provided above.