5.E: Exercises

CHEM U109 Chemistry of Living Things · LibreTexts

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    From LibreTexts, under CC BY-NC-SA 4.0, as the source states it; its equations are written in TeX, which the PDF shows typeset. This page at LibreTexts.

    1. Isooctane (C8H18) is used as a standard for comparing gasoline performance. (A) Write a balanced chemical equation for the combustion of isooctane. (B) if 12 isooctane molecules burn, how many CO2 molecules will be formed?

    2. Heptane (C7H16), like isooctane (see Exercise 1), is also used as a standard for determining gasoline performance. (A) Write a balanced chemical equation for the combustion of heptane. (B) How many oxygen molecules must have been used if 320 water molecules are formed by the combustion of heptane?

    3. What is the difference between a combination reaction and a redox reaction? Are all combination reactions also redox reactions? Are all redox reactions also combination reactions?

    4. A friend argues that the equation

      Fe2+ + Na → Fe + Na+

      is balanced because each side has one iron atom and one sodium atom. (A) Explain why your friend is incorrect. (B) Write and balance the half reactions and the overall reaction. (C) Which element is oxidized and which is the oxidizing agent?

    5. Historically, the first true battery was the Leclanché cell, named after its discoverer, Georges Leclanché. It was based on the following reaction:

      Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)

      Identify what is being oxidized, what is being reduced, and the respective reducing and oxidizing agents.

    Answers

    1. (A) 2C8H18 + 25O2 → 16CO2 + 18H2O ; (B) 96 CO2 molecules

    2. (A) C7H16 + 11O2 → 7CO2 + 8H2O ; (B) 440 O2 molecules

    1. A combination reaction makes a new substance from more than one reactant; a redox reaction exchanges (gains & loses) electrons. Not all combination reactions are redox reactions, and not all redox reactions are combination reactions.

    2. (A) Your friend is incorrect because the number of electrons transferring is not balanced.

    (B) Iron Half Reaction: Fe2+ + 2e- → Fe; Sodium Half Reaction: Na → Na+ + e- ; Overall Reaction: Fe2+ + 2Na → Fe + 2Na+

    (C) Na is oxidized and Fe2+ is the oxidizing agent.

     

    5.  Zinc (Zn) is oxidized and is the reducing agent. Copper (Cu2+) is reduced and is the oxidizing agent. 

    5.E: Exercises is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.