19. Assertion: A balanced chemical equation is essential for stoichiometric calculations. Reason: The coefficients of a balanced equation provide the mole ratios of the reacting species.

📘 Assertion–Reason Analysis

🔵 Assertion

A balanced chemical equation is essential for stoichiometric calculations.

Explanation: Stoichiometry deals with the quantitative relationship between reactants and products. These relationships are obtained from the coefficients of a balanced chemical equation.

2H₂ + O₂ → 2H₂O

This equation tells us that:

2 mol H₂ : 1 mol O₂ : 2 mol H₂O

🟠 Reason

The coefficients of a balanced chemical equation provide the mole ratios of the reacting species.

Explanation: In the equation above, the coefficients 2, 1 and 2 directly represent the mole ratio of H₂, O₂ and H₂O.

🎬 Mole Ratio Animation

H₂ H₂ + O₂ → H₂O H₂O

2 mol H₂ : 1 mol O₂ : 2 mol H₂O

The coefficients establish the mole ratio required for stoichiometric calculations.

🔗 Relationship Between Assertion & Reason

The Reason correctly explains why the Assertion is true.

Balanced Equation → Coefficients → Mole Ratio → Stoichiometric Calculation

✅ Final Answer

Both Assertion and Reason are TRUE, and Reason is the correct explanation of Assertion.

🎯 Key Concept

Balanced chemical equation → gives mole ratio → used for stoichiometric calculations.

Assertion–Reason Questions Directions: For each question, choose the correct option: A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion. B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion. C. Assertion is true, but Reason is false. D. Assertion is false, but Reason is true.

🧪 Assertion–Reason Questions

Directions:
For each question, choose the correct option:

A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

C. Assertion is true, but Reason is false.

D. Assertion is false, but Reason is true.

Assertion (A):
One mole of any substance contains 6.022 × 10²³ particles.

Reason (R):
Avogadro's number represents the number of particles present in one mole of a substance.

✅ Correct Answer: A

Both Assertion and Reason are true, and the Reason correctly explains the Assertion.

Assertion (A):
The molar mass of H₂O is 18 g mol⁻¹.

Reason (R):
H₂O contains two hydrogen atoms and one oxygen atom.

✅ Correct Answer: A

H₂O = (2 × 1) + (1 × 16) = 18 g mol⁻¹. The Reason explains the calculation of molar mass.

Assertion (A):
0.5 mole of a substance contains 3.011 × 10²³ particles.

Reason (R):
One mole contains 6.022 × 10²³ particles.

✅ Correct Answer: A

0.5 × 6.022 × 10²³ = 3.011 × 10²³ particles. Therefore, both statements are true and the Reason explains the Assertion.

Assertion (A):
Molarity changes with temperature.

Reason (R):
Molarity depends on the volume of the solution, and volume can change with temperature.

✅ Correct Answer: A

Molarity = Moles of solute / Volume of solution in litres. Since solution volume may change with temperature, molarity can also change.

Calculate the number of moles present in 18 g of H2O

📘 Step-by-Step Solution

Step 1: Given Data

Mass of H₂O = 18 g

We need to calculate the number of moles of H₂O.

Step 2: Calculate the Molar Mass of H₂O

Atomic masses:

H = 1 g mol⁻¹

O = 16 g mol⁻¹

Since H₂O contains 2 hydrogen atoms and 1 oxygen atom:

Molar Mass of H₂O

= (2 × 1) + (1 × 16)

= 2 + 16

= 18 g mol⁻¹

🎬 H₂O Molecular Animation

H H O

H₂O = 18 g mol⁻¹

One mole of H₂O has a mass of 18 grams.

Step 3: Use the Mole Formula

Number of moles (n) = Mass ÷ Molar Mass

Step 4: Substitute the Values

n = 18 ÷ 18

n = 1 mol

🎬 Mass → Moles Animation

18 g H₂O ÷ 18 g mol⁻¹ → 1 mol H₂O

Mass divided by molar mass gives the number of moles.

✅ Final Answer

Number of moles of H₂O = 1 mol

Therefore, 18 g of H₂O contains 1 mole of H₂O.

🎯 Quick Formula

n = m / M

n = 18 / 18

n = 1 mol