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Chemistry Chapter 9: Energy and Chemistry
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Chemistry Chapter 9: Energy and Chemistry

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Questions and Answers

What is considered waste energy in energy conversion?

  • Heat not converted to work (correct)
  • Electrical energy
  • Mechanical energy
  • Heat used efficiently
  • What is thermal pollution primarily caused by?

  • Reduced energy efficiency
  • Natural seasonal changes
  • Hot or cold waste streams (correct)
  • Efficient energy consumption
  • Which factor does NOT influence the amount of heat absorbed by a system?

  • The initial temperature (correct)
  • The temperature change
  • The mass of the material
  • The type of material
  • How is specific heat capacity represented for a substance?

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

    What does molar heat capacity indicate?

    <p>Heat required for one mole to raise by 1ºC</p> Signup and view all the answers

    Which of the following statements is true about specific and molar heat capacities?

    <p>Both are compound and phase specific</p> Signup and view all the answers

    What is the change in temperature represented by?

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

    Which method is used for observing and measuring heat flow into and out of a system?

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

    What does a nation's energy consumption indicate about its economic status?

    <p>It is directly related to economic growth.</p> Signup and view all the answers

    What percentage of energy consumption in the US was attributed to the industrial sector in 2011?

    <p>31%</p> Signup and view all the answers

    What is a significant cause of energy consumption during electricity generation?

    <p>Conversion losses</p> Signup and view all the answers

    In 2011, what was the total energy supply for the United States in quadrillion Btu?

    <p>107.66 quadrillion Btu</p> Signup and view all the answers

    Which form of energy accounted for the largest share of energy supply in 2011?

    <p>Natural gas</p> Signup and view all the answers

    What does the first law of thermodynamics state?

    <p>The total energy in a closed system remains constant.</p> Signup and view all the answers

    What is the primary use of nearly half of all domestic energy consumption?

    <p>Electricity production</p> Signup and view all the answers

    Which of the following energy sources accounted for the least portion of the total energy supply in 2011?

    <p>Natural gas liquids (NGPL)</p> Signup and view all the answers

    What is the sign of ΔH during an endothermic process such as vaporization?

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

    Which statement accurately describes ΔHcond?

    <p>It is an exothermic process.</p> Signup and view all the answers

    How is the enthalpy change calculated during a phase change?

    <p>ΔH = n x ΔH phase change</p> Signup and view all the answers

    What occurs during a phase change with respect to temperature?

    <p>Temperature remains constant.</p> Signup and view all the answers

    Which phase change is characterized by a positive ΔH value?

    <p>Melting of ice</p> Signup and view all the answers

    What is the relationship between ΔHvap and ΔHcond?

    <p>They are equal in magnitude but opposite in sign.</p> Signup and view all the answers

    In the process of heating ice to steam, which calculations are involved?

    <p>Both temperature change and phase change enthalpy calculations</p> Signup and view all the answers

    What is the unit of measurement for enthalpy changes during phase changes?

    <p>kJ/mol</p> Signup and view all the answers

    What does Hess's law state about the enthalpy change for a process?

    <p>It is independent of the particular way the process is carried out.</p> Signup and view all the answers

    What is a characteristic of a state function like enthalpy?

    <p>Its value depends only on the current state of the system.</p> Signup and view all the answers

    In calculating the enthalpy change using Hess's law, which of these can be considered?

    <p>Any convenient pathway between states.</p> Signup and view all the answers

    What is the enthalpy change represented by ΔH for the overall combustion of methane?

    <p>It is the same for both the direct and stepwise combustion processes.</p> Signup and view all the answers

    How is the enthalpy change for a reaction typically calculated using Hess's law?

    <p>By applying the formula ΔH = Σ v_i ΔH_f(products) - Σ v_j ΔH_f(reactants).</p> Signup and view all the answers

    What does the variable ΔH represent in enthalpy change calculations?

    <p>The change in enthalpy for a specified reaction.</p> Signup and view all the answers

    Which of the following is true about heat of formation reactions related to Hess's law?

    <p>They allow the calculation of enthalpy changes using standard values.</p> Signup and view all the answers

    What would be required to find the heat of combustion of propane using Hess's law?

    <p>Using tabulated standard enthalpies of formation for CO2 and H2O.</p> Signup and view all the answers

    What equation relates the heat flow in a calorimeter to the heat of the reaction?

    <p>qreaction = -qcalorimeter</p> Signup and view all the answers

    In calorimetry, an increase in temperature can be used to calculate the energy density of a fuel. How is energy density defined?

    <p>Energy liberated per gram of fuel burned.</p> Signup and view all the answers

    What is the primary difference between qv and qp when discussing the combustion of octane?

    <p>qp is measured at constant pressure, while qv is at constant volume.</p> Signup and view all the answers

    During an exothermic process, what can be said about ΔH?

    <p>ΔH is less than zero.</p> Signup and view all the answers

    What happens to the internal energy change (ΔE) in a system during an expansion?

    <p>ΔE equals q minus the work done by the system.</p> Signup and view all the answers

    Which equation accurately defines the change in enthalpy (ΔH)?

    <p>ΔH = DE + D(PV)</p> Signup and view all the answers

    For a calorimeter experiment, if the heater supplies 100.0 J of heat with a temperature change of 0.850°C, what can be inferred about the calorimeter's constant?

    <p>The calorimeter's heat capacity is 117.65 J/°C.</p> Signup and view all the answers

    In the context of a reaction under constant volume, which equation represents the relationship between internal energy change (ΔE) and heat flow (q)?

    <p>ΔE = q</p> Signup and view all the answers

    Study Notes

    Chapter 9: Energy and Chemistry

    • Economic growth is closely correlated with a nation's energy consumption, represented through Gross Domestic Product (GDP).
    • In 2011, the United States had an energy supply of 107.66 quadrillion Btu, with significant contributions from coal, natural gas, crude oil, nuclear, and renewable sources.
    • Domestic production in 2011 accounted for 70.47 quadrillion Btu, while imports contributed 31.02 quadrillion Btu.
    • Energy consumption distribution in the U.S. was as follows: residential (22%), commercial (19%), industrial (31%), and transportation (28%).
    • Approximately two-thirds of the energy consumed for electricity generation is wasted due to conversion losses.
    • Thermal pollution results from waste heat altering the temperature of water bodies, impacting ecosystems.
    • Calorimetry is the technique used to measure heat flow in chemical reactions, with various dependencies including mass, type of material, and temperature change.
    • Specific heat capacity (c) measures heat needed to raise 1 gram of a substance by 1ºC; molar heat capacity (Cp) applies to 1 mole of a substance.
    • The formula for heat energy absorbed is represented as: ( q_{calorimeter} = C_{calorimeter} \times \Delta T_{calorimeter} ) and ( q_{reaction} = -q_{calorimeter} ).

    Enthalpy Concepts

    • Enthalpy (H) is the heat content of a system and is calculated using the relation ( H = E + PV ).
    • Changes in enthalpy, ( \Delta H ), indicate whether a reaction is exothermic (releases heat, ( \Delta H < 0 )) or endothermic (absorbs heat, ( \Delta H > 0 )).
    • Phase changes at constant pressure are characterized by enthalpy changes; boiling and freezing involve heat of vaporization (( \Delta H_{vap} )) and heat of condensation (( \Delta H_{cond} )).
    • ( \Delta H ) for phase changes is substance-specific and measured in kJ/mol, calculated using the number of moles involved.

    Hess’s Law and Thermodynamic Calculations

    • Hess's law states the total enthalpy change for a reaction is independent of its pathway; only the initial and final states matter.
    • Enthalpy changes can be calculated using tabulated data of standard molar enthalpies of formation.
    • The formula for calculating enthalpy change for a reaction via Hess’s law is: [ \Delta H = \sum v_i \Delta H_f (products) - \sum v_j \Delta H_f (reactants) ]
    • Practical examples include calculating the heat of combustion for various reactants, demonstrating the application of Hess’s law.

    Example Problems

    • Problems illustrate the use of calorimetry to determine energy density and the enthalpy changes related to phase transitions and chemical reactions, enhancing understanding of thermodynamic principles.

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    Description

    Explore the relationship between energy consumption and economic growth in this quiz focused on Chapter 9 of Chemistry. Learn about energy sources, consumption distribution in the U.S., and the concepts of calorimetry and thermal pollution. Test your understanding of how energy impact chemical processes and ecosystems.

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