Enthalpy Changes Flashcards
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Questions and Answers

What is enthalpy defined as?

  • Measure of heat energy present in a chemical reaction (correct)
  • The pressure of a gas
  • A measure of temperature in reactions
  • None of the above

    • What is enthalpy change?

    Amount of energy released/taken in during a chemical reaction (cannot be measured)

    An exothermic reaction releases energy into its surroundings.

    True

    What is the symbol for an exothermic reaction?

    <p>-∆H</p> Signup and view all the answers

    An endothermic reaction releases energy from its surroundings.

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

    What is the symbol for an endothermic reaction?

    <p>+∆H</p> Signup and view all the answers

    What is activation energy?

    <p>Minimum energy required for a reaction to take place</p> Signup and view all the answers

    What is the symbol for enthalpy change under standard conditions?

    <p>∆H^θ</p> Signup and view all the answers

    What are the standard conditions in chemistry?

    <p>100kPa, 298K and the standard state of the substance</p> Signup and view all the answers

    What is enthalpy change of reaction?

    <p>Enthalpy change for a reaction when molar quantities of reactants react together</p> Signup and view all the answers

    What is enthalpy change of formation?

    <p>Enthalpy change associated with the formation of 1 mole of a compound from its elements</p> Signup and view all the answers

    What is enthalpy change of combustion?

    <p>Enthalpy change associated with the complete combustion of 1 mole of substance</p> Signup and view all the answers

    What is the enthalpy change of neutralization?

    <p>Enthalpy change associated with the formation of 1 mole of water from a neutralisation reaction between acid and base</p> Signup and view all the answers

    What is the ionic equation for all strong base and strong acid reactions?

    <p>H⁺ + OH⁻ = H₂O</p> Signup and view all the answers

    What is the enthalpy change of neutralization for strong acids and bases?

    <p>∆neutH = -57</p> Signup and view all the answers

    How is ∆neutH calculated?

    <p>q / moles of water</p> Signup and view all the answers

    What is the calculation rule for enthalpy change reactions?

    <p>Bond breaking - bond making</p> Signup and view all the answers

    What is the formula to calculate enthalpy change of formation?

    <p>∆H2 - ∆H1</p> Signup and view all the answers

    What is the formula to calculate enthalpy change of combustion?

    <p>∆H1 - ∆H2</p> Signup and view all the answers

    Bond breaking is endothermic.

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

    Bond making is exothermic.

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

    How is Delta H calculated?

    <p>Products - reactants</p> Signup and view all the answers

    Study Notes

    Enthalpy Concepts

    • Enthalpy measures the heat energy involved in a chemical reaction.
    • Enthalpy change quantifies the energy released or absorbed during a reaction and cannot be directly measured.
    • Exothermic reactions release energy to the surroundings, indicated by a negative enthalpy change symbol (-∆H).
    • Endothermic reactions absorb energy from the surroundings, denoted by a positive enthalpy change symbol (+∆H).

    Activation Energy

    • Activation energy is the minimum energy needed to initiate a reaction, primarily to break bonds.

    Standard Conditions

    • Enthalpy change under standard conditions is represented as ∆H^θ.
    • Standard conditions include a pressure of 100 kPa, a temperature of 298 K, and the standard state of a substance (e.g., O₂ as a gas).

    Types of Enthalpy Change

    • Enthalpy change of reaction refers to the change occurring when molar quantities of reactants react together.
    • Enthalpy change of formation is the change related to forming one mole of a compound from its elements.
    • Enthalpy change of combustion involves the complete combustion of one mole of a substance.
    • The enthalpy change of neutralization refers to the formation of one mole of water from a neutralization reaction between an acid and a base.

    Neutralization Reactions

    • The ionic equation for reactions between strong acids and bases is H⁺ + OH⁻ = H₂O.
    • Since all strong acid-base reactions have the same ionic equation, the enthalpy change of neutralization is consistently -57 kJ/mol.

    Calculating Enthalpy Changes

    • To calculate the enthalpy change of neutralization (∆neutH), use the formula q (heat absorbed/released) divided by the moles of water produced.
    • The general rule for calculating enthalpy changes in reactions is bond breaking - bond making, remembering to consider the signs.
    • The formula to calculate enthalpy change of formation is ∆H2 - ∆H1.
    • The formula for enthalpy change of combustion is ∆H1 - ∆H2.

    Bond Energy

    • Bond breaking is associated with an endothermic process, which requires energy input.
    • Bond making is exothermic, releasing energy during bond formation.

    Delta H Calculation

    • The change in enthalpy (ΔH) is determined by subtracting the total energy of reactants from the total energy of products, resulting in either a positive or negative value.

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    Description

    Explore the fundamental concepts of enthalpy changes in chemical reactions through these flashcards. Each card provides a key term and its definition, aiding in the understanding of exothermic reactions and enthalpy calculations.

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