Sconesnatcher Posted April 22, 2009 Share Posted April 22, 2009 (edited) Heres a practice chemistry test to prepare us for the real one next week. Heres how Id answer the questions Q1) What is meant by the Heat of Formation of a substance? The heat of formation is the enthalpy changed when 1 mole of a compound is formed from its elements Q2) Calculate the heat of formation of methane from the following data: C + O2 CO2 DH = -393kJ/mol H2 + 1/2O2 H2O DH = -280kJ/mol CH4 + 2O2 CO2 + 2H2O DH = -895kJ/mol Not sure what this one means. WHat have those reactions got to do with methane? 3.) Draw an energy profile diagram that illustrates an exothermic reaction and include in the diagram the effect of a catalyst 4.)Describe an experiment that would illustrate the effect of concentration on the rate of a chemical reaction 5.) Describe an experiment that would be carried out to examine the electrolysis of water This one I'd just say "Running current through a hoffman apparatus filled with water will produce hydrogen gas at one electrode and oxygen gas at the other. To verify the presence of hydrogen air can be released from the apparatus and caught in a jar. A flame is then applied to the jar and if it ignites it indicates the presence of hydrogen gas and verifies that electrolysis of water has taken place. 5b) Write out the chemical equations for the reactions at both the cathode and the anode 5c) Why is dilute acid used? 5d.) A current of 0.75 amperes flows through an aqueous solution of silver nitrate for one hour and 45 minutes. What mass of silver is deposited during this electrolysis 5e.) What property of metals is illustrated in an electrode potentials table 5f.) What does the following chemical equation tell you about the relative positions of copper and iron in the electrochemical series? Fe + CuSO4 Cu + FeSO4 more to come Edited April 22, 2009 by Sconesnatcher Link to comment Share on other sites More sharing options...
CaptainPanic Posted April 23, 2009 Share Posted April 23, 2009 (edited) Heres a practice chemistry test to prepare us for the real one next week. Heres how Id answer the questions Q1) What is meant by the Heat of Formation of a substance? The heat of formation is the enthalpy changed when 1 mole of a compound is formed from its elements Correct. Q2) Calculate the heat of formation of methane from the following data:C + O2 CO2 DH = -393kJ/mol H2 + 1/2O2 H2O DH = -280kJ/mol CH4 + 2O2 CO2 + 2H2O DH = -895kJ/mol Not sure what this one means. WHat have those reactions got to do with methane? CH4 = methane. You have to combine the reactions so that you make the formation of methane form its elements. Then also recombine the heats of reactions to form the heat of formation. 3.) Draw an energy profile diagram that illustrates an exothermic reaction and include in the diagram the effect of a catalyst Study the term "activation energy" (hint: google/wikipedia). 4.)Describe an experiment that would illustrate the effect of concentration on the rate of a chemical reaction You don't need help with this one I hope. Just realize that "an experiment" is not necessarily 1 single reaction. You can do many reactions in 1 single experiment. 5.) Describe an experiment that would be carried out to examine the electrolysis of waterThis one I'd just say "Running current through a hoffman apparatus filled with water will produce hydrogen gas at one electrode and oxygen gas at the other. To verify the presence of hydrogen air can be released from the apparatus and caught in a jar. A flame is then applied to the jar and if it ignites it indicates the presence of hydrogen gas and verifies that electrolysis of water has taken place. Sounds good. 5b) Write out the chemical equations for the reactions at both the cathode and the anode 5c) Why is dilute acid used? 5d.) A current of 0.75 amperes flows through an aqueous solution of silver nitrate for one hour and 45 minutes. What mass of silver is deposited during this electrolysis 5e.) What property of metals is illustrated in an electrode potentials table 5f.) What does the following chemical equation tell you about the relative positions of copper and iron in the electrochemical series? Fe + CuSO4 Cu + FeSO4 more to come We're not going to answer your homework questions - I've given some hints and hopefully you can solve your questions now. mod note: moved to HW help by swansont Edited April 23, 2009 by swansont add mod note 1 Link to comment Share on other sites More sharing options...
Sconesnatcher Posted April 26, 2009 Author Share Posted April 26, 2009 Thanks. Thats all I was asking for a few comments on how I was doing. Link to comment Share on other sites More sharing options...
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