Topic 5: Energetics Flashcards

1
Q

Define the standard enthalpy of combustion.

A

The enthalpy change for the complete combustion of one mole of a substance in its standard state in excess oxygen under standard conditions. ∆H = kJmol-1. EXOTHERMIC.

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2
Q

Define the standard enthalpy change of reaction.

A

The enthalpy change when the reactants in a stoichiometric equation react, under standard conditions, to form the products. ΔHr.

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3
Q

Define the standard enthalpy neutralisation.

A

The enthalpy change when one mole of water is formed by the reaction of an acid with alkali under standard conditions. ΔHneutral. EXOTHERMIC.

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4
Q

Define Hess’s law.

A

The enthalpy change for any chemical reaction is independent of the route providing the starting conditions and the final conditions (and reactants and products) are the same.

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5
Q

What are the conditions for standard enthalpy changes?

A

Temperature = 298 KPressure = 100 kPa1 mol dm-3 solutions

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6
Q

Define the bond enthalpy.

A

The energy needed to break one mole of bonds in gaseous molecules under standard conditions.

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7
Q

Define the enthalpy of formation.

A

The enthalpy change when one mole of product is formed from its constituent elements in their standard states.

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8
Q

Define the enthalpy ionisation energy.

A

The standard enthalpy change that occurs on the removal of 1 mole of electrons from 1 mole of gaseous atoms or positively charged ions. ENDOTHERMIC.

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9
Q

Define first electron affinity.

A

The energy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous ions under standard conditions. EXOTHERMIC.

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10
Q

Define lattice enthalpy.

A

The enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under standard conditions (i.e. lattice to ions). ENDOTHERMIC.

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11
Q

Define enthalpy of atomisation/sublimation.

A

The enthalpy change that occurs when one mole of gaseous atoms is formed from the element in its standard state (i.e. standard state to gas). ENDOTHERMIC.

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12
Q

Define enthalpy of solution.

A

The enthalpy change when 1 mole of a solute dissolves in sufficient water to form an infinitely dilute solution.*Two steps - lattice enthalpy and enthalpy of hydration.

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13
Q

Define enthalpy of hydration.

A

The enthalpy change when one mole of gaseous ions is dissolved to form an infinitely dilute solution of one mole of aqueous ions (i.e. ions from gas to aqueous). EXOTHERMIC.

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14
Q

Define enthalpy of dissociation.

A

The amount of energy required to break a chemical bond between two species.

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15
Q

Define entropy.

A

The distribution of available energy among the particles. *Measure of disorder. Ordered states (eg. solids) have low entropy, disordered states (eg. gases) have high entropy.

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16
Q

What is Gibbs free energy?

A

Combination of entropy and enthalpy of a system. It is negative for a SPONTANEOUS process, positive for a NON-SPONTANEOUS process and zero if the system is at equilibrium.

17
Q

What type of reaction occurs when bonds are broken?

A

Endothermic.

18
Q

Describe the bonding in ozone.

A

The bonds in ozone are intermediate in strength and length between a single and a double bond. They are broken down by UV radiation < 330nm. Bond order 1.5.

19
Q

Describe the bonding in oxygen.

A

The oxygen molecule has a double covalent bond. Bond order 2 (stronger than ozone!) It is broken down by UV radiation of < 242nm.