Physical Chapter 4: Energetics Flashcards

1
Q

What is Enthalpy change defined as?

A

The heat energy transferred in a reaction at a constant pressure.
(weird theta symbol means standard conditions & standard states)

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2
Q

What is the value for delta H if a reaction is endothermic?

A

positive

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3
Q

What is the value for delta H if a reaction is exothermic?

A

Negative

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4
Q

What type of bond enthalpy do you use for calculations?

A

Mean bond enthalpy

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5
Q

What is standard enthalpy of formation defined as?

A

The enthalpy change when 1 mole of a compound is formed frfom its elements in their standard states under standard conditions

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6
Q

What is standard enthalpy of combustion defined as?

A

The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions.

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7
Q

What is calorimetry?

A

You burn a fuel or undertake a neutralisation reaction, and measure the temperature change, using this value to calculate the enthalpy change.

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8
Q

What is a good method to obtain an accurate temperature change from calorimetry?

A

Draw a graph and extrapolate from the beginning of the reaction

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9
Q

WHy can you not just use starting temperature and end temperature in calorimetry to find temperature change?

A

Heat will have been lost to the surroundings - this will not be 100% accurate

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10
Q

What formula do you use to find emthalpy changes?

A

Q = mc(delta)T

Q - heat lost (joules)
m = mass in g
c = specific heat capacity
T = temperature (Kelvin)

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11
Q

What is Hess’s law?

A

Total enthalpy change is the same regardless of the route taken

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12
Q

How can we use Hess’s Law?

A

We can find out enthalpy changes frfom enthalpy of formation or combustion to find alternative routes

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