Chemical Reactions Observations
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Questions and Answers

What indicates that a chemical reaction has occurred?

  • Change in temperature (correct)
  • Change in shape
  • No evolution of gas
  • No change in color

    • Which type of equation shows the change from reactants to products?

  • Arithmetical equation
  • Symbolic equation
  • Chemical reaction equation
  • Word-equation (correct)

    • In the reaction between magnesium and oxygen, which of the following is the product?

  • Oxygen
  • Hydrogen
  • Magnesium oxide (correct)
  • Magnesium

    • What is shown on the left-hand side of a word-equation?

    <p>Reactants with plus signs</p> Signup and view all the answers

    Which of the following does NOT suggest a chemical reaction has occurred?

    <p>Physical mixing of substances</p> Signup and view all the answers

    What term describes the substances that undergo change in a chemical reaction?

    <p>Reactants</p> Signup and view all the answers

    In a reaction, what does the arrow in a word-equation represent?

    <p>The direction of the reaction</p> Signup and view all the answers

    How is the reaction of magnesium burning in oxygen expressed in word-equation form?

    <p>Magnesium + Oxygen → Magnesium oxide</p> Signup and view all the answers

    What type of reaction occurs when ferrous sulphate decomposes upon heating?

    <p>Decomposition reaction</p> Signup and view all the answers

    Which of the following is NOT a product of the thermal decomposition of ferrous sulphate?

    <p>Calcium oxide (CaO)</p> Signup and view all the answers

    What happens to the ferrous sulphate crystals when heated?

    <p>They change color and lose water.</p> Signup and view all the answers

    What is a common use of calcium oxide produced from the decomposition of calcium carbonate?

    <p>Manufacturing cement</p> Signup and view all the answers

    During the thermal decomposition of lead nitrate, which gas is emitted?

    <p>Nitrogen dioxide (NO2)</p> Signup and view all the answers

    The process of heating to induce decomposition reactions is referred to as what?

    <p>Thermal decomposition</p> Signup and view all the answers

    Which of the following is a characteristic of decomposition reactions?

    <p>They break down a single reactant into simpler products.</p> Signup and view all the answers

    Which of the following statements about the decomposition of calcium carbonate is true?

    <p>It results in the formation of calcium oxide and carbon dioxide.</p> Signup and view all the answers

    In the reaction CuO + H2 → Cu + H2O, what occurs to copper(II) oxide?

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

    What defines an oxidation-reduction (redox) reaction?

    <p>One reactant is reduced while the other is oxidised.</p> Signup and view all the answers

    During the reaction ZnO + C → Zn + CO, what happens to carbon?

    <p>It is oxidised to CO.</p> Signup and view all the answers

    What happens to manganese dioxide (MnO2) in the reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2?

    <p>It is reduced to MnCl2.</p> Signup and view all the answers

    When a substance gains oxygen during a reaction, what is it said to undergo?

    <p>Oxidation.</p> Signup and view all the answers

    What occurs during the rusting of iron?

    <p>Iron is oxidised to form a reddish brown coating.</p> Signup and view all the answers

    What is the green coating formed on copper due to corrosion?

    <p>Copper patina.</p> Signup and view all the answers

    What effect does gaining hydrogen have on a substance in a chemical reaction?

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

    What is the correct number of hydrogen molecules needed to balance the equation in the first step?

    <p>4 molecules of H2</p> Signup and view all the answers

    After balancing hydrogen atoms, what element remains to be balanced in the equation?

    <p>Iron</p> Signup and view all the answers

    How many atoms of iron are initially present in the reactants for balancing?

    <p>1</p> Signup and view all the answers

    What is the balanced equation that results after all elements are balanced?

    <p>3 Fe + 4 H2O → Fe3O4 + 4 H2</p> Signup and view all the answers

    What method is employed for balancing the chemical equations as discussed?

    <p>Hit-and-trial method</p> Signup and view all the answers

    Which physical state is represented by the symbol (aq) in chemical equations?

    <p>Aqueous solution</p> Signup and view all the answers

    What notation is used to indicate a substance in the gaseous state in a chemical equation?

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

    Why is it important to mention the physical states of reactants and products in a chemical equation?

    <p>To make the equation more informative</p> Signup and view all the answers

    Which statement about the reaction 2PbO(s) + C(s) → 2Pb(s) + CO2(g) is correct?

    <p>Lead is getting oxidised.</p> Signup and view all the answers

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

    <p>Displacement reaction.</p> Signup and view all the answers

    When dilute hydrochloric acid is added to iron fillings, what products are formed?

    <p>Hydrogen gas and iron chloride.</p> Signup and view all the answers

    Which of the following correctly describes oxidation?

    <p>Gain of oxygen.</p> Signup and view all the answers

    Why should chemical equations be balanced?

    <p>To ensure mass is conserved.</p> Signup and view all the answers

    What is produced when calcium hydroxide reacts with carbon dioxide?

    <p>Calcium carbonate and water.</p> Signup and view all the answers

    Which of these equations is correctly balanced?

    <p>HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O.</p> Signup and view all the answers

    What is the product of the reaction between zinc and silver nitrate?

    <p>Zinc nitrate and silver.</p> Signup and view all the answers

    Study Notes

    Observations of Chemical Reactions

    • Changes indicating a chemical reaction include: change in state, color shift, gas evolution, and temperature change.
    • Various chemical reactions occur in daily life, prompting a study of their types and symbolic representations.

    Chemical Equations

    • A chemical reaction can be expressed through word equations that summarize the transformation of reactants to products, e.g.:
      • Magnesium + Oxygen → Magnesium oxide
    • Reactants are listed on the left and products on the right, separated by an arrow.

    Balancing Chemical Equations

    • Balancing ensures the number of atoms for each element remains equal on both sides of the equation.
    • Initial equations may require balancing through trial and adjustments using smallest whole number coefficients.
    • Use of symbols for physical states enhances chemical equations:
      • (g) for gas, (l) for liquid, (aq) for aqueous, (s) for solid.

    Types of Reactions

    • Decomposition reactions involve a single reactant breaking down into simpler products, e.g.,:
      • CaCO3(s) → CaO(s) + CO2(g)
    • Thermal decomposition requires heat, illustrated through various examples.

    Redox Reactions

    • Oxidation involves the gain of oxygen or loss of hydrogen; reduction involves the loss of oxygen or gain of hydrogen.
    • In reaction dynamics, one reactant is oxidized while another is reduced, classified as redox reactions.
    • Examples include:
      • CuO + H2 → Cu + H2O

    Corrosion and Its Effects

    • Corrosion often manifests as rusting in iron and tarnishing in metals like copper and silver, affecting their appearance.
    • Oxidation-reduction reactions also characterize processes of corrosion.

    Exercises on Chemical Reactions

    • Understand and identify incorrect statements regarding specific reactions.
    • Recognize different reaction types (combination, displacement, decomposition) through provided examples.

    Practice with Chemical Equations

    • Translate statements into chemical equations, ensuring to balance them accurately.
    • Familiarize with balancing techniques and identify types of reactions, enhancing overall comprehension of chemical processes.

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    Chemical Reactions and Equations PDF

    Description

    This quiz explores the observations that indicate a chemical reaction has taken place, including changes in temperature, state, and color. Participate to test your understanding of the key signs of chemical reactions.

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