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Edexcel Chemistry > Topic 8 - Chemical energetics > Flashcards

Topic 8 - Chemical energetics Flashcards

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1
Q

What is enthalpy?

A

The heat energy stored within a chemical system

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2
Q

What is enthalpy change?

A

The heat energy exchange with the surroundings in a reaction at standard room temperature and pressure

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3
Q

What does exothermic mean?

A

where heat energy is transferred to the surroundings from the system

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4
Q

What does endothermic mean?

A

where heat energy is transferred from the surroundings to the system

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5
Q

Define the enthalpy change of reaction

A

The enthalpy change of a reaction at standard room temperature and pressure

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6
Q

Define the enthalpy change of formation

A

The enthalpy change where 1 mole of a compound is produced from its constituent elements in their standard states

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7
Q

Define enthalpy change of combustion

A

The enthalpy change where 1 mole of a substance is burned in excess oxygen under standard conditions

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8
Q

Define enthalpy change of neutralisation

A

The enthalpy change where 1 mole of water is produced by neutralisation at standard room temperature and pressure

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9
Q

What is calorimetry?

A

A process that allows us to calculate the ENERGY CHANGE by measuring the temperature change of a known volume of water/solution

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10
Q

Outline the process of experimental determination of enthalpy change of combustion of a liquid

A
  1. A spirit burner containing the the liquid under test is weighed.
  2. A known volume of water is added to a copper can
  3. The temperature of the water is measured
  4. The burner is lit
  5. The mixture is constantly stirred with a therometer
  6. When the temperature of the water has reached approximately 20 degrees above its original temperature, the flame is extinguished and the burner is immediately reweighed
  7. The final temperature is measured
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11
Q

What are potential sources of error in the experiment to determine the enthalpy change of combustion of a liquid

A
  • Some heat energy produced in burning is transferred to the air and not the water
  • Some of the ethanol may not burn completely to form carbon dioxide and water (incomplete combustion would cause soot to form on the bottom of the can)
  • Some of the heat energy produced is transferred to the copper can and not the water
  • The conditions are not standard (water vapour, not liquid water, is produced)
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12
Q

Outline the experimental determination of enthalpy change of neutralisation

A

Wear safety glasses and a lab coat
Place a known volume and concentration of acid into a polystyrene cup
Measure the temperature of the acid
Using a pipette, place a known volume of alkali into a beaker
Measure the temperature of the alkali
Add the acid and alkali, stir with the thermometer and measure the maximum temperature reached

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13
Q

What are the potential sources of error and assumptions made in the experiment to determine enthalpy change of neutralisation

A

Uncertainties of measurements involved with the use of the pipette and the thermometer.
Some heat energy will be transferred to the thermometer and the polystyrene cup

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14
Q

What is Hess’s law?

A

The enthalpy change for a reaction is independent of the route taken in converting reactants into products, provided the initial and final concentrations are the same in each case

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15
Q

Why do we use Hess’s law?

A

Most standard enthalpy changes of formation cannot be determined experimentally

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16
Q

What is bond enthalpy?

A

The average energy required/released when 1 mole of covalent bonds are broken/formed

17
Q

What is mean bond enthalpy?

A

The enthalpy change when one mole of a bond, averaged out over many different molecules is broken

18
Q

What is mean bond enthalpy?

A

The enthalpy change when one mole of a bond, averaged out over many different molecules is broken

19
Q

What type of reaction is breaking bonds?

A

Endothermic

20
Q

What type of reaction is making bonds?

A

Exothermic

21
Q

Draw an energy profile diagram for an exothermic reaction

A
  • Energy of reactants is higher than the energy of products
  • enthalpy change is negative (energy released to surroundings)
  • label activation energy
22
Q

Draw an energy profile diagram for an endothermic reaction

A
  • Energy of products is higher than the energy of the reactants
  • enthalpy change is positive (energy is taken in from the surroundings)
  • label activation energy
23
Q

What is the first law of thermodynamics?

A

During a chemical reaction energy cannot be created or destroyed, only converted from one form of energy to another

24
Q

What is kinetic energy?

A

A measure of the motion of particles (atoms, molecules or ions) in a substance

25
Q

What is potential energy?

A

A measure of how strongly these particles interact with one another (both attract or repel one another)

26
Q

What is Lattice dissociation enthalpy?

A

The enthalpy change when one mole of a solid ionic compound is completely dissociated into its gaseous constituent ions under standard conditions.

27
Q

Is lattice dissociation enthalpy exo or endothermic?

A

Endothermic

28
Q

What is lattice formation enthalpy?

A

The enthalpy change when one mole of a solid ionic compound is formed from its constituent ions under standard conditions.

29
Q

Is lattice formation enthalpy exo or endothermic?

A

Exothermic

30
Q

What is atomisation enthalpy?

A

The energy required for the formation of one mole of gaseous atoms from an element under standard conditions.

31
Q

What is enthalpy of electron affinity?

A

The enthalpy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous 1- ions under standard conditions.

32
Q

What does the perfect ionic model assume?

A
  • All the ions are perfectly spherical
  • Charge is distributed evenly throughout the ion
  • The ions display no covalent character
33
Q

What is enthalpy of solution?

A

The enthalpy change when one mole of ionic solid is dissolved in water to produce a solution of infinite dilution under standard conditions.

34
Q

What does infinite dilution mean?

A

The constituent ions of ionic substance no longer interact.

35
Q

What is enthalpy of hydration

A

The enthalpy change when one mole of gaseous ions is dissolved in water to produce one mole of aqueous ions under standard conditions.
(this value is nearly always negative as water molecule have delta + regions that naturally attract negative ions)

Edexcel Chemistry (3 decks)

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