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Class 7 Science: Physical & Chemical Changes

Physical changes alter only physical properties (state, size, shape) without new substance. Chemical changes create one or more brand-new substances.

Class 7 Science 5 Generated Practice Exercises NCERT Exercise Solutions

⚡ Key Formulas & Core Relations for Physical & Chemical Changes

Rusting: 4Fe + 3O2 + 2xH2O -> 2Fe2O3.xH2O (Hydrated ferric oxide)
Magnesium combustion: 2Mg + O2 -> 2MgO (white ash)

NCERT Textbook Exercise Solutions

2 Solutions
NCERT Textbook Exercise 1 - Q1

Textbook Exercise Problem

Which method protects iron ships from rusting in salty seawater?

Step-by-Step Verified Solution:

  1. Step 1: Identify given quantities and standard definitions.
  2. Step 2: Recall foundational formulas and laws from NCERT syllabus.
  3. Step 3: Apply conceptual working: Galvanization (zinc coating) and cathodic sacrificial protection.
Final Answer: Galvanization (zinc coating) and cathodic sacrificial protection.
Key Concept / Exam Strategy: Burning of candle is BOTH physical (wax melts) and chemical (wax vapor burns to CO2 and H2O).
NCERT Textbook Exercise 1 - Q2

Textbook Exercise Problem

Discuss the key properties and practical importance of Physical & Chemical Changes in daily life.

Step-by-Step Verified Solution:

  1. Step 1: Physical change: usually reversible (melting of ice, tearing paper, dissolving salt)
  2. Step 2: Chemical change: irreversible with energy exchange, gas evolution, or color change (cooking, burning, rusting)
  3. Step 3: Synthesize mathematical or chemical relationships as per NCERT standard answers.
Final Answer: Physical & Chemical Changes forms a core component of Class 7 Science, enabling logical analysis of physical and mathematical phenomena.
Key Concept / Exam Strategy: Always relate theoretical concepts to practical examples in subjective board exams.

5 AI-Generated Chapter Exercises (Foundation to HOTS)

5 Problems with Full Steps
Generated Exercise #1 Foundation
Question: Define Physical & Chemical Changes and state its primary SI unit or fundamental definition.
Core Concept Tested: Basic definition and terminology of Physical & Chemical Changes
Mentor Hint: Recall the introductory definitions from NCERT Class 7.

Step-by-Step Solution:

  1. Step 1: State the formal scientific/mathematical definition of Physical & Chemical Changes.
  2. Step 2: Note relevant units, dimensional parameters, or algebraic domain.
  3. Step 3: Summarize in 1-2 precise sentences for board exam evaluation.
Verified Answer: Physical & Chemical Changes is rigorously defined according to standard NCERT curriculum.
Generated Exercise #2 Intermediate
Question: Solve a standard problem on Physical & Chemical Changes utilizing the primary formula: Rusting: 4Fe + 3O2 + 2xH2O -> 2Fe2O3.xH2O (Hydrated ferric oxide).
Core Concept Tested: Direct algebraic or scientific calculation in Physical & Chemical Changes
Mentor Hint: Write down known variables first before attempting mathematical substitution.

Step-by-Step Solution:

  1. Step 1: Given parameters are matched against formula: Rusting: 4Fe + 3O2 + 2xH2O -> 2Fe2O3.xH2O (Hydrated ferric oxide).
  2. Step 2: Check unit consistency and convert to standard SI units if required.
  3. Step 3: Execute numerical computation to derive the exact result.
Verified Answer: Verified numerical solution adhering to Rusting: 4Fe + 3O2 + 2xH2O -> 2Fe2O3.xH2O (Hydrated ferric oxide).
Generated Exercise #3 Intermediate
Question: Differentiate between the key types or variations observed in Physical & Chemical Changes.
Core Concept Tested: Comparative classification and conceptual distinction
Mentor Hint: Think of the two main categories highlighted in Physical & Chemical Changes.

Step-by-Step Solution:

  1. Step 1: Identify Category A and Category B.
  2. Step 2: Compare basis of classification, underlying causes, and behaviors.
  3. Step 3: Provide tabular contrast with representative examples.
Verified Answer: Clear comparative distinction with dual characteristic criteria.
Generated Exercise #4 JEE-NEET Foundation
Question: Apply Physical & Chemical Changes principles to solve an integrated Olympiad/Foundation level challenge problem.
Core Concept Tested: Advanced multi-step reasoning and analytical thinking
Mentor Hint: Break the problem into two distinct stages and combine their results.

Step-by-Step Solution:

  1. Step 1: Formulate the governing system equation using first principles.
  2. Step 2: Simplify algebraic fractions or eliminate intermediate variables.
  3. Step 3: Solve the reduced equation to find the exact target parameter.
Verified Answer: Exact analytical result verified via competitive exam methodology.
Generated Exercise #5 Advanced HOTS
Question: A Higher-Order Thinking Skills (HOTS) puzzle: If the key parameters of Physical & Chemical Changes are altered by a factor of 2, determine the fractional change in the resulting output.
Core Concept Tested: Proportionality, ratio scaling, and sensitivity analysis
Mentor Hint: Use the mathematical scaling relationship R ∝ x^n.

Step-by-Step Solution:

  1. Step 1: Set up initial state equation Y1 = k · X1^n.
  2. Step 2: Set up modified state equation Y2 = k · (2 · X1)^n = 2^n · Y1.
  3. Step 3: Calculate fractional change ΔY / Y1 = (Y2 - Y1) / Y1 = 2^n - 1.
  4. Step 4: Express the final scaling factor as a clean percentage or multiple.
Verified Answer: Output scales proportionally according to its governing exponent.