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CHEMISTRY > 5.2 ENERGETICS > Flashcards

5.2 ENERGETICS Flashcards

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1
Q

Define an enthalpy change of a reaction

A

The heat energy it releases or absorbs per mole

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2
Q

Is heat energy absorbed or released in an ENDOthermic reaction (and so what enthalphy sign is it)

A

Absorbed (+)

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3
Q

Is heat energy absorbed or released in an EXOthermic reaction (and so what enthalphy sign is it)

A

Released (-)

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4
Q

Units of enthalpy

A

kJ/mol

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5
Q

How do you draw an energy level diagram for an ENDOthermic reaction

A
  • Enthalpy scale on y-axis, and time/progression on x-axis
  • Reactants drawn on line on bottom of diagram
  • Vertical line up with an arrow (labelled with enthalpy)
  • Products of horizontal line above line
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6
Q

How do you draw an energy level diagram for an EXOthermic reaction

A
  • Enthalpy scale on y-axis, and time/progression on x-axis
  • Reactants drawn on line at top of diagram
  • Vertical line down with an arrow (labelled with enthalpy)
  • Products of horizontal line below
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7
Q

When bonds are broken, what type of reaction is it

A

Endothermic

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7
Q

When bonds are broken, what type of reaction is it

A

Endothermic - energy is absorbed

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8
Q

When bonds are made, what type of reaction is it

A

Exothermic - energy is released

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9
Q

Unit for bond energy

A

kJ/mol

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10
Q

Equation for calculating with bond energies

A

Enthalpy change = Bonds broken - bonds made

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11
Q

How to calculate a bond energy question

A
  • Add up each individual bond energy for each bond
  • Add them together for products and reactants
  • Subtract products from reactants
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12
Q

In an exothermic reaction, what is the ‘ratio’ of energy absorbed / released

A

Released > Absorbed

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12
Q

In an exothermic reaction, what is the ‘ratio’ of energy absorbed / released

A

Released > Absorbed

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13
Q

In an endothermic reaction, what is the ‘ratio’ of energy absorbed/released

A

Absorbed > Released

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14
Q

In an endothermic reaction, what is the ‘ratio’ of energy absorbed/released

A

Absorbed > Released

15
Q

What is the activation energy

A

The energy needed to break the bonds

16
Q

How do you make an energy level diagram, a reaction profile diagram

A
  • There is a hump from the products to the reactants
  • In the centre of the hump, and arrow up
  • Labelled activation energy and the actual enthalpy (if avaliable)
17
Q

Q =

A

Q=mc 0t

18
Q

Enthalpy Change equation

A

-Q / moles

19
Q

Describe how to carry out a combustion calorimetry experiment

A
  • Weigh 50g of water and plae in a can above a burner
  • Measure inital mass of burner and intital temperature of water
  • Ignite the burner, stir water for 30s then extinguish burner
  • Measure final mass of burner, and final temperature of water
20
Q

How to calculate enthalpy change from a combustion calorimetry experiment

A
  • Q=mc0t (of water)
  • CONVERT TO KJ
  • Moles of fuel
  • Enthalpy = -Q/moles
20
Q

What are the main sources of error in a combustion calorimetry experiment

A
  • Heat loss - most of the thermal energy heats the air
  • Incomplete combustion - releases less heat energy
21
Q

How do endothermic reactions get given a ‘+’ value for enthalpy change when being calculated

A

Q=mc0t will be negative and so -Q/mol (negative multipied by negative) will be positive

22
Q

Describe how to carry out a solution calorimetry experiment

A
  • Pipette 25cm^3 of solution into polystyrene cup
  • Measure intital temperature of solution
  • Add 1g of metal and stir continuosly
  • Mesure the maximum temperature of solution
22
Q

Describe how to carry out a solution calorimetry experiment

A
  • Pipette 25cm^3 of solution into polystyrene cup
  • Measure intital temperature of solution
  • Add 1g of metal and stir continuosly
  • Mesure the maximum temperature of solution
23
Q

What are the sources of error in a solution calorimetry experiment

A
  • Heat loss - thermal energy used to heat up air
  • Incomplete reaction - not stired/left for long enough
  • Solution is no longer pure water - won’t have same SHC

CHEMISTRY (17 decks)

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