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Chemistry AS Module 2 > Energetics > Flashcards

Energetics Flashcards

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1
Q

What is enthalpy?

A

The total thermodynamic energy in a system

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2
Q

What is △H for an exothermic reaction?

A

-ve

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3
Q

What is △H for an endothermic reaction?

A

+ve

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4
Q

What are four endothermic reactions?

A

Melting, boiling, evaporation and sublimination

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5
Q

What are two exothermic reactions?

A

Freezing and condensation

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6
Q

Draw the enthalpy level diagram for an endothermic reaction

A

in book

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7
Q

Draw the enthalpy level diagram for an exothermic

reaction

A

in book

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8
Q

What are standard conditions?

A

298K and 100kPa

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9
Q

What are the units for enthalpy

A

kJmol^-1

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10
Q

When working out standard enthalpy of combustion and given combustion values what should you do?

A

You should keep the combustion values the same but flip the sign of the enthalpy of formation values as you are trying to work out standard enthalpy of combustion

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11
Q

What state are the reactants and products in when writing equations?

A

All in their standard states at 298K and 100atm pressure

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12
Q

What is the definition of standard enthalpy of combustion?

A

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

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13
Q

Standard enthalpy of formation?

A

The enthalpy change when one mole of a compound is from its elements under standard conditions

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14
Q

Standard enthalpy of neutralisation

A

The enthalpy change when one mole of water is produced in a neutralisation reaction under standard conditions

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15
Q

What is the equation for standard enthalpy of neutralisation

A

H+(aq) + OH-(aq) → H20(l)

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16
Q

What should you do when calculation enthalpy of formation when given formation values?

A

Keep the formation values the same but flip the signs of the combustion values as you are trying to work out the enthalpy of formation

17
Q

What is the expression for converting temperature change to energy?

A

q = MC△T

and then use △H = (q÷1000) ÷ moles

18
Q

What do each of the letters represent?

A

q - energy change in JOULES
m - mass in grams of the substance causing the temperature change
c - specific heat capacity (4.2 Jg-1cm3-1)
△T - temperature change (ºC or Kelvin)

19
Q

Why do you divide by 100 and moles when calculating enthalpy change?

A

To change it from joules to kJ and the per mole of substance

20
Q

How do you determine the enthalpy of neutralisation?

A
  1. Add an exact volume of known concentration of alkali into a polystyrene cup and measure the initial temperature
  2. Add an exact volume of a known concentration of acid to the cup while stirring
  3. Measure the highest temperature reached and calculate temperature change △T
  4. Calculate energy change ( q=mc△T)
  5. Then calculate energy per one moles of water using
    △H = (q÷1000) ÷ mols
21
Q

How do you determine the enthalpy of combustion?

A
  1. Measure the mass of liquid fuel used
  2. Measure the initial temperature of a known volume of water in a beaker
  3. Allow the fuel in spirit burner to burn and heat the water
  4. Measure the highest temperature reached and calculate temperature change
  5. Calculate energy change using q=mc△T
  6. Calculate enthalpy for one mole using
    △H = (q÷1000)÷moles
22
Q

Draw a labelled diagram for both enthalpy of combustion and enthalpy of neutralisation

A

in book

23
Q

What is Hess’s law?

A

The enthalpy change for a reaction is independent of the route taken, provided the initial and final conditions are the same.

24
Q

What is average bond enthalpy measured in and what should you do when answering questions on it?

A

Measured in kJmol-1 and you should draw out all the bonds

25
Q

What is bond breaking and bond making?

A

Bond breaking is endothermic (+△H) and bond making is exothermic (-△H)

26
Q

When answering question what should you do

A

Work out the total number of bonds, multiply by the enthalpy and then put a negative sign in front of the bonds make as that process if exothermic.

Chemistry AS Module 2 (11 decks)

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