Chemistry Chapter on Enthalpy Changes
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Questions and Answers

What does the symbol $ riangle H$ represent in a chemical reaction?

  • Change in temperature
  • Change in pressure
  • Change in volume
  • Change in enthalpy (correct)

    • Formation enthalpy refers to the energy change when a chemical compound is broken down into its elements.

    False

    What is the formula for calculating the change in enthalpy ($ riangle H$) of a reaction?

    $ riangle H = ext{sum of (n} riangle H^°){products} - ext{sum of (n} riangle H^°){reactants}$

    The energy required to form a chemical compound is called its __________.

    <p>formation enthalpy</p> Signup and view all the answers

    Match the terms to their definitions:

    <p>Enthalpy Change = The difference between the enthalpy of products and reactants Formation Enthalpy = Energy change associated with the formation of a compound $ riangle H$ = Symbol representing change in enthalpy Reactants = Substances consumed in a chemical reaction</p> Signup and view all the answers

    What does a standard molar enthalpy of formation (ΔH°) of 0 kJ/mol indicate?

    <p>The substance is a pure element</p> Signup and view all the answers

    A compound with a higher standard molar enthalpy of formation is more thermally stable than one with a lower value.

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

    What is the significance of the negative value of ΔH° for a compound like sucrose (C12H22O11)?

    <p>It indicates that energy is released when the compound is formed.</p> Signup and view all the answers

    The lower (more negative) the value of a compound's standard molar enthalpy of formation, the more ________ it is.

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

    Match the following compounds with their standard molar enthalpy of formation values:

    <p>Sucrose (C12H22O11) = -2226.1 kJ/mol Oxygen (O2) = 0 kJ/mol Carbon (C) = 0 kJ/mol Water (H2O) = -285.8 kJ/mol</p> Signup and view all the answers

    What is the standard molar enthalpy of formation for hexane?

    <p>-198.7 kJ/mol</p> Signup and view all the answers

    The combustion of ethanol produces only carbon dioxide and water.

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

    What is the enthalpy change sign for the combustion of ethanol?

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

    The balanced equation for the combustion of ethanol is C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(g). The enthalpy change has a _______ sign.

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

    Match the following chemical compounds with their respective chemical formulas:

    <p>Ethanol = C₂H₅OH Carbon dioxide = CO₂ Water = H₂O Hexane = C₆H₁₄</p> Signup and view all the answers

    Which diagram appropriately represents the combustion of methanol in a closed system?

    <p>Diagram B</p> Signup and view all the answers

    The enthalpy change for the reaction CH₄(g) + 2H₂O(g) → CO₂(g) + 4H₂(g) is +658.8 kJ per mole of hydrogen.

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

    What is the enthalpy change ($ riangle H$) for the reaction involving methane and water producing carbon dioxide and hydrogen?

    <p>+164.7 kJ</p> Signup and view all the answers

    The equation to calculate enthalpy change is: $ riangle{H} = ext{sum of } riangle{H}{products} - ext{sum of } riangle{H}{reactants}$, which is based on the principle of _____ in thermodynamics.

    <p>energy conservation</p> Signup and view all the answers

    Match the enthalpy values to their respective descriptions:

    <p>+164.7 kJ = Enthalpy change of the reaction +658.8 kJ/mol = Enthalpy change per mole of hydrogen</p> Signup and view all the answers

    What does Hess' Law state about the total enthalpy change for a chemical reaction?

    <p>It is independent of the route of the reaction.</p> Signup and view all the answers

    Hess' Law can be compared to a journey having multiple routes with different start and end points.

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

    Who formulated Hess' Law?

    <p>Germain Henri Hess</p> Signup and view all the answers

    According to Hess' Law, the total enthalpy change for a reaction can be expressed as ΔHnet = ΔH1 + ΔH2 + ΔH3... where ΔHnet represents the ________ change.

    <p>net enthalpy</p> Signup and view all the answers

    Match the following concepts to their descriptions:

    <p>Hess' Law = Enthalpy change is independent of the reaction route ΔHnet = Total enthalpy change of a chemical reaction Enthalpy = Heat content of a system Route = Path taken in a reaction</p> Signup and view all the answers

    What is the standard enthalpy change (ΔH) for the reaction that forms hexane?

    <p>-109.3 kJ</p> Signup and view all the answers

    The reaction C₂H₄(g) + H₂(g) → C₂H₆(g) has a ΔH of -136.8 kJ.

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

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

    <p>-285.8 kJ</p> Signup and view all the answers

    The reaction C(s) + O₂(g) → CO₂(g) has an enthalpy change (ΔH) of _____ per mole of C.

    <p>-393.5 kJ</p> Signup and view all the answers

    Match the given reactions with their respective enthalpy changes:

    <p>C₂H₄(g) + 3 O₂(g) → 2 CO₂(g) + 2 H₂O(l) = -1411 kJ C₂H₆(g) + 7/2 O₂(g) → 2 CO₂(g) + 3 H₂O(l) = -1560 kJ (flipped) H₂(g) + 1/2 O₂(g) → H₂O(l) = -285.8 kJ C(s) + O₂(g) → CO₂(g) = -393.5 kJ</p> Signup and view all the answers

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