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Chemistry: Energetics > Enthalpy > Flashcards

Enthalpy Flashcards

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1
Q

What is enthalpy change?

A

Measure of heat change at a constant pressure

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2
Q

What are the standard conditions for enthalpy?

A

Pressure: 100kPa
Temperature: 298K

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3
Q

What is meant by the standard molar enthalpy of formation?

A

Enthalpy change when one mole substance is formed from constituent elements under standard conditions and all reactants and products in standard states

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4
Q

What is meant by the standard molar enthalpy of combustion?

A

Enthalpy change when one mole substance is completely burnt in oxygen under standard conditions with all reactants and products in standard states

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5
Q

What is temperature and how is it measured?

A

Related to average kinetic energy of the particles in a system
Measured using thermometer

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6
Q

What is heat a measure of?

A

Total energy of all particles present in given amount of substance

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7
Q

What do you need to know to measure enthalpy change?

A

-mass of substance heated/cooled
-temperature change
-specific heat capacity of substance

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8
Q

What is specific heat capacity?

A

Amount of heat to raise temperature of 1g substance by 1K

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9
Q

What is the specific heat capacity of water?

A

4.18 Jg-1K-1

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10
Q

How is enthalpy change calculated ( word equation) ?

A

Enthalpy change = mass of substance * specific heat capacity * temperature change

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11
Q

What equation is used to calculate enthalpy change (symbol equation) ?

A

q = mc^t

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12
Q

What is q?

A

Enthalpy change

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13
Q

What is m?

A

Mass of substance (g)

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14
Q

What is c?

A

Specific heat capacity (Jg-1K-1)

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15
Q

What is ^t?

A

Change in temperature (K)

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16
Q

How is q=mc^t rearranged for m?

A

m=q/c^t

17
Q

How is q=mc^t rearranged for c?

A

c=q/m^t

18
Q

How is q=mc^t rearranged for ^t?

A

^t=q/mc

19
Q

How does the simple calorimeter experiment measure enthalpy change?

A

using spirit burner of ethanol heat known mass of water
record initial temperature of water and weight of spirit burner
note temperature rise in water
re-weigh spirit burner
calculate temperature change
use equation q=mc^t

20
Q

How is delta H calculated?

A

delta H = q/mol

21
Q

What methods are applied to reduce and allow for heat loss?

A

-use copper calorimeter or polystyrene cup as they are good insulators
-use draught excluder
-use thermometer which reads to 0.1 C
-create cooling curve

22
Q

How is a cooling curve created?

A

-measure temperature every 30s for 4 minutes
-don’t record temperature at 4 minutes, add solutions together
-record temperature every 30s for further 6 minutes
-draw graph time against temperature
-extrapolate line of best fit to 4 minutes
-find temperature change

Chemistry: Energetics (4 decks)

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