Question 1

Question 4What is a balanced chemical equation? Why should chemical equations be balanced?

Accepted Answer

A balanced equation is one in which the number of atoms of each element of the reactant is equal to the number of atoms of each element of the products.An equation must be balanced in order to comply with the "Law of Conservation of Mass", which states that mass is neither created nor destroyed in the course of a chemical reaction. An unbalanced equation would imply that atoms have been created or destroyed.

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Chapter 1: Chemical Reactions and Equations &mdash; Quick Revision Guide

Introduction
      Chemical reactions are processes where substances interact to form new substances with different properties. This chapter covers the writing and balancing of chemical equations, types of chemical reactions, and the real-world effects of oxidation.

Key Points at a Glance
      
        A chemical equation represents a reaction using symbols and formulae with state symbols (s), (l), (g), (aq)
        Equations must be balanced &mdash; same number of atoms of each element on both sides (Law of Conservation of Mass)
        Combination: Two or more substances combine into one product. Example: CaO + H2O &rarr; Ca(OH)2
        Decomposition: One substance breaks into two or more. Types: thermal, electrolytic, photolytic. Example: 2FeSO4 &rarr; Fe2O3 + SO2 + SO3
        Displacement: More reactive element displaces less reactive from its compound. Example: Fe + CuSO4 &rarr; FeSO4 + Cu
        Double displacement: Exchange of ions between two compounds. Example: Na2SO4 + BaCl2 &rarr; BaSO4&darr; + 2NaCl
        Redox: Simultaneous oxidation (gain of O / loss of H) and reduction (loss of O / gain of H). Example: CuO + H2 &rarr; Cu + H2O
        Corrosion: Slow destruction of metals by environment &mdash; rusting of iron (Fe2O3&middot;xH2O); prevention: painting, oiling, galvanising, alloying
        Rancidity: Oxidation of fats/oils giving bad taste/smell; prevention: antioxidants, airtight containers, refrigeration, nitrogen flushing

Real-World Connections
      Respiration is oxidation of glucose; digestion involves decomposition; formation of curd from milk is a chemical change; fireworks involve combination reactions; electroplating is a redox process.

Quick Self-Test (5 Questions)
      
        What is the most important concept you learned from this chapter?
        Can you write three key equations/formulae from this chapter from memory?
        Draw a labelled diagram relevant to this chapter without looking at your notes.
        Explain one real-world application of a concept from this chapter.
        What is one common mistake students make in this chapter, and how can you avoid it?

Further Study
      
        NCERT Textbook Chapter 1
        NCERT Exemplar Problems
        Bright Tutorials Detailed Notes: ch01-chemical-reactions.html
        Bright Tutorials Practice Questions: ch01-chemical-reactions.html
        Previous Year CBSE Board Papers

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Question 2

Question 5Translate the following statements into chemical equations and then balance them.(a) Hydrogen gas combines with nitrogen to form ammonia.(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Accepted Answer

(i) 3H2 (g) + N2 (g) ⟶ 2NH3 (g)(ii) 2H2S (g) + 3O2 (g) ⟶ 2H2O (l) + 2SO2 (g)(iii) 3BaCl2 (aq) + Al2(SO4)3 (aq) ⟶ 2AlCl3 (aq) + 3BaSO4 (s)(iv) 2K (s) + 2H2O (l) ⟶ 2KOH (s) + H2 (g)