Measuring enthalpy changes pt 2

Question 1

How are enthalpy changes measured in a reaction that takes place in a solution?

Answer 1

Easy to measure

The heat is generated in the solutions themselves and only has to be kept in a calorimeter

Expanded polystyrene beakers are foten used, as they are good insulators of heat and a low heat capacity.

The specific heat capacity of dilute solutions is usually taken to be the same as that of water

Question 2

What is the nature of a neutralisation reaction?

Answer 2

Exothermic

Question 3

How can heat loss be allowed?

Answer 3

When comparing the enthalpy changes of two reagents, do it in the same conditions

Question 4

what are the controls when measuring the change of enthalpy in solution? and precautions

Answer 4

• same conditions
• insulate
  
  • minimise heat transfer to surrounbding
• stir regularly to ensure reaction goes to completion
• immerse bulb of thermomenter
• use lid

Question 5

What if a solid reagent is used?

Answer 5

• add the ssolutioon to the cup first then add the solid weighed out on a balance

Question 6

What are the errors in the investigation?

Answer 6

• heat loss / gain
• approximation of heat capacity of soln
  
  • taken as waters
• neglecting heat capacity of the calorimeter
• incomplete reaction
• assuming density of soln the same as water

Question 7

How does change in heat energy relate to change in enthalpy?

Answer 7

• H = E + PV
  
  • E = internal energy
  • PV = energy to push surrounding
• on Earth / constant pressure
  
  • ΔH = q
    
    • if a reaction released 74kJ of heat, the enthalpy change is equal to that
  • q = heat absorbed or released in a reaction
  • all change in heat is caused by a change in enthalpy (assumed)

Question 8

What causes the change in enthalpy during a reaction

Answer 8

• when bonds moves to higher or lower energy states - endo/exo