6.4.2 Enthalpies of Formation Flashcards Preview

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Flashcards in 6.4.2 Enthalpies of Formation Deck (11)
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1
Q

enthalpies of formation

A
  • The standard enthalpy change ( H°) gives the enthalpy change for a reaction performed at standard state and a given temperature.
  • The standard molar enthalpy of formation describes the standard enthalpy change for the formation of one mole of a compound from its elements.
  • Hess’s law can be used to calculate the standard enthalpy change for a reaction from the standard molar enthalpies of formation of the reactants and products.
2
Q

note

A
  • The standard enthalpy change ( H°) gives the enthalpy
    change for a reaction performed at standard state and is
    reported for 25 °C, since it depends on temperature.
  • At standard state substances are in their most stable form at 1 atmosphere of pressure at the given temperature.
  • When substances have different allotropes such as carbon (e.g. graphite and diamond), the most stable form is used (graphite).
  • The standard molar enthalpy of formation describes the
    standard enthalpy change for the formation of one mole of a compound from its elements.
  • Standard formation reactions begin with reactants that are elements in their standard states and produce one mole of product.
  • Because they form only one mole of product, standard
    formation reactions often contain fractional coefficients.
  • The standard molar enthalpy of formation for an element in standard state is zero.
3
Q

Which of the following statements is not true about allotropes?

A

Allotropes have different forms at room temperature, but the same enthalpy.

4
Q

Which of the following best describes the standard enthalpy change?

A

The enthalpy change with all the reactants and products in their standard state

5
Q

Which of the following is true about a standard formation reaction?

A

A standard formation reaction results in exactly 1 mole of product.

6
Q

Which of the following statements is not true?

A

The standard enthalpy of formation for a pure element in its standard state is +1

7
Q

Which of the following is(are) true about the standard enthalpy change of formation?

A
  • Standard enthalpy change of formation also referred to as the standard heat of formation.
  • Standard enthalpy change of formation the standard enthalpy change to prepare 1 mole of a compound from the elements in their standard state.
  • Standard enthalpy change of formation is written ΔH°f .
8
Q

Which of the following statements about a standard enthalpy change is true?

A

An enthalpy change with all the reactants and products in their standard state

9
Q

What is the temperature and pressure most often used to determine standard states?

A

25°C, 1 atm

10
Q

Which of the following is not a standard enthalpy of formation reaction?

A

CaO(s) + CO2(g) -> CaCO2(s)

11
Q

Which of the following is not a standard enthalpy of formation reaction?

A

2H2(g) + O2(g) → 2H2O(l)

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