Topic 5 Flashcards

1
Q

What is heat?

A

Form of energy that can be transferred from a higher to lower temperature object

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2
Q

What is temperature?

A

Average Ek of particles in a substance

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3
Q

What is enthalpy?

A

The heat absorbed or released in a chemical reaction at constant pressure

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4
Q

Can enthalpy be measured?

A

No only enthalpy change

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5
Q

What is standard enthalpy change?

A

The enthalpy change of a reaction carried out under standard conditions with everything in its standard state ( 100 kPA, 298 k)

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6
Q

Features of a exothermic reaction

A
  • Energy is released to the surrondings
  • Temp of the surrondings increases
  • Combustion and nuetralisation
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7
Q

Draw an enthalpy diagram for exothermic reaction

A
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8
Q

Features of an endothermic diagram

A
  • temperature of surrondings decrease
  • energy is taken in
  • thermal decomposition and photosynthesis
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9
Q

What is the equation for energy

A

q=mc delta t

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10
Q

What is the equation for enthalpy change?

A

Delta H = q/n

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11
Q

Assumptions of calorimetry

A
  • Assume there is no heatloss to the surrondings and the calorimeter
  • Assume that the SHC is the same as water
  • Assume that the combustion is complete
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12
Q

What is standard enthalpy change of formation

A

When one mole of a compound is formed from its constituent elements in their standard states with everything under standard conditions

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13
Q

What is the formula for enthalpy change?

A

Enthalpy change = sum of standard enthalpy change of formation of products - sum of standard enthalpy change of reactants

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14
Q

What is standard enthalpy change of combustion?

A

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

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15
Q

Draw a basic enthalpy cycle diagram

A
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16
Q

What are the rules for Hess’s law

A
  • DO everything in relation to the final equation

- Compare the 1st and 3rd when cancelling

17
Q

What is the definition for average bond enthalpy?

A

The energy required to break one mole of a bond in a gaseous molecule averaged over similar compounds

18
Q

Why is bond enthalpy less accurate than using standard formation to find the enthalpy change?

A

Because it is an average

19
Q

How do you use bond enthalpy to work out delta H?

A

Reactants - products
OR
Bonds broken - bonds formed

20
Q

Acronym for making and breaking bonds

A

MEXOBENDO

21
Q

Write the equations for the destruction of ozone?

A

O2 – O. + O.
O.+ O2 – O3
O3– O2+ O.
O3+ O. –2O2

22
Q

Compare the structures of oxygen and ozone

A
  • O3 is a resonance structure and has a bond order of 1.5

- The double bond in O2 is stronger than the one in O3 which means it requires more energy to break