Balancing Chemical Equations

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Questions and Answers

What is the criteria for selecting the compound to start balancing in the given equation?

  • The compound that contains the most abundant element
  • The compound with the minimum number of atoms
  • The compound with the most electro-negative element
  • The compound with the maximum number of atoms (correct)

What is the correct way to balance oxygen atoms in the given equation?

  • Add a coefficient of 4 to Fe3O4
  • Change the formula of H2O to H2O4
  • Change the formula of Fe3O4 to FeO4
  • Add a coefficient of 4 to H2O (correct)

Why is it necessary to remember that the formulae of the compounds or elements involved in the reactions cannot be altered?

  • To ensure the reaction is reversible
  • To increase the reaction rate
  • To maintain the stoichiometry of the reaction (correct)
  • To ensure the reaction is irreversible

What is the reason for making the number of molecules of hydrogen as four on the RHS?

<p>To equalise the number of H atoms (D)</p> Signup and view all the answers

What is the mistake in balancing the equation if we change the formula of H2O to H2O4?

<p>It will alter the stoichiometry of the reaction (B)</p> Signup and view all the answers

What is the correct statement about the number of atoms of different elements in the unbalanced equation?

<p>The number of O atoms is 4 on the RHS and 1 on the LHS (C)</p> Signup and view all the answers

What is the purpose of listing the number of atoms of different elements in the unbalanced equation?

<p>To determine the stoichiometry of the reaction (B)</p> Signup and view all the answers

What is the correct partly balanced equation after balancing the oxygen atoms?

<p>Fe + 4H2O → Fe3O4 + H2 (A)</p> Signup and view all the answers

What is the term for a reaction in which a single product is formed from two or more reactants?

<p>Combination reaction (C)</p> Signup and view all the answers

What is the chemical formula for marble?

<p>CaCO3 (C)</p> Signup and view all the answers

What is the characteristic of a reaction that releases heat, like the burning of coal?

<p>Exothermic (D)</p> Signup and view all the answers

What is the general equation for the formation of water from hydrogen and oxygen?

<p>2H2(g) + O2(g) → 2H2O(l) (B)</p> Signup and view all the answers

What is the purpose of using a solution of slaked lime for white washing walls?

<p>To form a thin layer of calcium carbonate on the walls (D)</p> Signup and view all the answers

What is the chemical equation for the reaction of calcium hydroxide with carbon dioxide?

<p>Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) (D)</p> Signup and view all the answers

What is the term for the process of breaking down food into simpler substances during digestion?

<p>Digestion (D)</p> Signup and view all the answers

What is the chemical equation for the burning of natural gas?

<p>CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) (B)</p> Signup and view all the answers

What does the notation (aq) represent in a chemical equation?

<p>Aqueous solution in water (A)</p> Signup and view all the answers

Why are physical states not included in a chemical equation unless necessary?

<p>To make the equation more concise (A)</p> Signup and view all the answers

What is the result of the reaction between copper oxide and hydrogen gas?

<p>Copper oxide is reduced and hydrogen is oxidised. (A)</p> Signup and view all the answers

What is the purpose of writing the reaction conditions above and/or below the arrow in a chemical equation?

<p>To provide additional information about the reaction conditions (C)</p> Signup and view all the answers

What is the common feature of the reactions shown in equations (1.28) and (1.29)?

<p>Both are oxidation-reduction reactions. (C)</p> Signup and view all the answers

Which of the following statements is true about reaction (1.31)?

<p>Carbon is oxidised to CO. (D)</p> Signup and view all the answers

Which of the following equations is correctly balanced?

<p>3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g) (D)</p> Signup and view all the answers

What is the correct state symbol for steam in a chemical equation?

<p>(g) (B)</p> Signup and view all the answers

What is the oxidation state of iron in the reaction 2Fe2O3 + 2Al → Al2O3 + 2Fe?

<p>0 (D)</p> Signup and view all the answers

What happens to the substance that loses oxygen during a reaction?

<p>It is reduced. (A)</p> Signup and view all the answers

Why is it necessary to clean a magnesium ribbon before burning in air?

<p>To remove impurities that may affect the reaction (C)</p> Signup and view all the answers

What is the result of the reaction between manganese dioxide and hydrochloric acid?

<p>MnO2 is reduced and HCl is oxidised. (B)</p> Signup and view all the answers

What type of reaction is 2Fe2O3 + 2Al → Al2O3 + 2Fe?

<p>Displacement reaction (A)</p> Signup and view all the answers

What is the product of the reaction between dilute hydrochloric acid and iron fillings?

<p>Iron chloride and water (B)</p> Signup and view all the answers

What is the purpose of using state symbols in a chemical equation?

<p>To specify the physical state of reactants and products (D)</p> Signup and view all the answers

Which of the following is a characteristic of an oxidation-reduction reaction?

<p>One reactant gets oxidised while the other gets reduced. (A)</p> Signup and view all the answers

Why should chemical equations be balanced?

<p>To conserve mass and follow the law of conservation of mass (A)</p> Signup and view all the answers

Which of the following equations is an example of a reaction that requires a catalyst?

<p>6CO2(aq) + 12H2O(l) → C6H12O6(aq) + 6O2(aq) + 6H2O(l) (A)</p> Signup and view all the answers

What happens to the substance that gains oxygen during a reaction?

<p>It is oxidised. (D)</p> Signup and view all the answers

What is the correct balanced equation for the reaction between hydrogen gas and nitrogen to form ammonia?

<p>3H2 + N2 → 2NH3 (A)</p> Signup and view all the answers

What is the general term for the reaction in which one reactant gets oxidised and the other gets reduced?

<p>Oxidation-reduction reaction. (B)</p> Signup and view all the answers

What is the oxidation state of barium in the reaction BaCl2 + H2SO4 → BaSO4 + HCl?

<p>+2 (B)</p> Signup and view all the answers

What is the correct balanced equation for the reaction between calcium hydroxide and carbon dioxide to form calcium carbonate and water?

<p>Ca(OH)2 + CO2 → CaCO3 + H2O (D)</p> Signup and view all the answers

What is the oxidation state of zinc in the reaction Zn + 2AgNO3 → Zn(NO3)2 + 2Ag?

<p>+2 (D)</p> Signup and view all the answers

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Study Notes

Balancing Chemical Equations

  • To balance a chemical equation, start by listing the number of atoms of each element in the reactants and products.
  • Identify the compound with the maximum number of atoms and select the element with the maximum number of atoms in that compound.
  • To balance the atoms, use coefficients in front of the formulas of the compounds, but never change the formulas of the compounds or elements involved in the reaction.

Steps to Balance a Chemical Equation

  • Step I: Write the unbalanced equation.
  • Step II: List the number of atoms of different elements present in the unbalanced equation.
  • Step III: Balance the atoms by using coefficients in front of the formulas of the compounds.
  • Step IV: Check and balance the remaining atoms.

Chemical Reactions

  • Combination reactions: when two or more substances (elements or compounds) combine to form a single product.
  • Examples of combination reactions:
    • Burning of coal: C(s) + O2(g) → CO2(g)
    • Formation of water from H2(g) and O2(g): 2H2(g) + O2(g) → 2H2O(l)
  • Exothermic reactions: reactions that release heat along with the formation of products.
  • Examples of exothermic reactions:
    • Burning of natural gas: CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
    • Respiration: a process that releases energy from the food we eat

Oxidation-Reduction Reactions

  • Oxidation: when a substance gains oxygen during a reaction.
  • Reduction: when a substance loses oxygen during a reaction.
  • Examples of oxidation-reduction reactions:
    • CuO + H2 → Cu + H2O
    • ZnO + C → Zn + CO
    • MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
  • If a substance gains oxygen or loses hydrogen during a reaction, it is oxidized. If a substance loses oxygen or gains hydrogen during a reaction, it is reduced.

Types of Chemical Reactions

  • Combination reaction: when two or more substances combine to form a single product.
  • Displacement reaction: when one element displaces another element from a compound.
  • Decomposition reaction: when a single compound breaks down into two or more simpler substances.
  • Double displacement reaction: when two compounds react to form two new compounds.

Chemical Equations

  • A balanced chemical equation is a representation of a chemical reaction that shows the number of atoms of each element in the reactants and products.
  • Chemical equations should be balanced to satisfy the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
  • Balanced chemical equations can be used to predict the amount of reactants required and the amount of products formed in a reaction.

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