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Enthalpy change Flashcards

(18 cards)

1
Q

What is enthalpy?

A

Heat content in a substance

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2
Q

What is enthalpy change?

A

the heat energy change at constant pressure

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3
Q

What is the difference between a closed system and an open system?

A

closed system = only exchanges energy not matter
open system = exchanges energy and matter

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4
Q

How do you calculate enthalpy change?

A

heat content of products - heat contents of reactants
or
heat energy change/number of moles of reactant

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5
Q

What does enthalpy change depend on?

A

pressure and temperature

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6
Q

What are standard states and conditions?

A
  • elements or compounds in their normal physical state e.g: chlorine gas or water liquid
  • pressure of 100kPa / 1 atm
  • temperature of 25°C (298K)
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7
Q

What is standard enthalpy change of formation?

A

the enthalpy change when one mole of the compound in its standard state is formed from its constituent elements under standard conditions. e.g: H2(g) + 1/2O2 -> H2O

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8
Q

What is standard enthalpy change of combustion?

A

the enthalpy change when one mole of the substance burns completely under standard conditions e.g: C3H8(g) + 5O2 -> 3CO2 + 4H2O

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9
Q

Why is the standard enthalpy change of formation of an element always 0?

A

By definiton

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10
Q

If a reaction is endothermic, what will the energy level diagram look like?

A

Products are higher than reactants

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11
Q

If a reaction is exothermic, what will the energy level diagram look like?

A

Products are lower than reactants

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12
Q

If a reaction is exothermic what will the enthalpy change be?

A

negative

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13
Q

If a reaction is endothermic what will the enthalpy change be?

A

positive

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14
Q

What is enthalpy change measured in?

A

kJmol-1

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15
Q

Define standard enthalpy change of a reaction

A

The heat energy change measured under standard conditions

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16
Q

What is the equation used to calculate heat energy change from experimental data?

17
Q

What is average bond enthalpy?

A

when one mole of a covalent bond is broken in gaseous conditions