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Chemistry Unit 2 > Thermochemistry > Flashcards

Thermochemistry Flashcards

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0
Q

What is the molar bond enthalpy?

A

The energy required to break a mole of bonds

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1
Q

When are covalent molecules formed?

A

When the electrons shared between atoms result in a lower energy system than the atoms alone before bonding. This process is exoteric and has a negative enthalpy change.

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2
Q

Bond enthalpies always refer to breaking bonds under what conditions?

A

Gaseous

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3
Q

What is Hess’s law?

A

The overall reaction enthalpy is the sum of the reaction enthalpies of each step of the reaction

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4
Q

What is the first law of thermodynamics?

A

Energy is conserved

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5
Q

What is the standard enthalpy change?

A

And enthalpy change for a reaction in which reactants and products are considered to be in their standard states at a specified temp

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6
Q

What is the standard state of a substance?

A

The most stable state of the substance under standard conditions

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7
Q

What do the standard conditions refer to?

A

A pressure of one atmosphere and a specific temp, usually 298K (25 degrees Celsius)

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8
Q

What is the standard molar enthalpy of formation (

A

The enthalpy change that occurs when one mole of a substance is prepared from its elements in their standard states

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9
Q

What is the standard molar enthalpy of combustions (

A

The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions. It’s always negative since combustion is exothermic

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10
Q

What is the strength of covalent bonds measured by?

A

The bond enthalpy

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11
Q

What is the standard molar enthalpy change of lattice formation? (

A

The comparable enthalpy value for ionic compounds.
The enthalpy change that occurs when 1 mole of an ionic crystal is formed from the ions in their gaseous state under standard conditions.

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12
Q

How can the lattice enthalpy be calculated from Hess’s law?

A

The sum of (e) deltaH by route one = the sum of deltaH by route two

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13
Q

What are the two steps in the process of an ionic compound dissolving?

A

1) energy has to be supplied to break the lattice = endothermic
2) free ions become surrounded by water molecules. The formation of new bonds releases energy - solvation

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14
Q

What is the enthalpy of solution? (DeltaHsoln)

A

The enthalpy change when 1 mole of a substance is dissolved completely in water

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15
Q

What is the enthalpy of hydration ? (DeltaHhyd)

A

The enthalpy change when one mole of individual gaseous ions is completely hydrated

16
Q

What is the standard molar enthalpy of sol of an ionic compound that involves lattice and hydration enthalpy steps given by?

A

DeltaHsoln = deltaHhyd - deltaHlatt

Chemistry Unit 2 (7 decks)

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