Energetics Flashcards
(12 cards)
What is the experiment for the enthalpy of neutralisation?
Set volume of acid in a polystyrene cup
Volume = mass as water density is 1
Record initial temp every min for 3
Add alkali on 4 but don’t record temp
Carry on for 15 mins recording temp
Draw a graph, temp v time and draw 2 lines of best fit
Vertical line at 4th minute for change in temp
How do you work out the change in enthalpy after a neutralisation experiment and after the graph has been drawn?
Work out q (change in energy) by q=mc x change in temp
Work out moles using the mass of solid or moles of liquid then use the equation
Change in enthalpy per mole = q/n to work out enthalpy change
Don’t forget the sign - for exothermic, + for endothermic
What is the experiment for the enthalpy for a solid and a liquid?
Weigh out metal/metal carbonate/anhydrous compound with a weighing boat (Mass with - mass of just boat after)
Calculate the moles with the Mr
Add set volume of liquid (acid or water) to a polystyrene cup
Record temp every min for 3
On 4 add the metal/metal carbonate/anhydrous compound but don’t record temp
Carry on until 15 mins recording temp
Draw a graph of temp v time with 2 lines of best fit and work out change in temp with a vertical line at 4 mins
How to work out change in enthalpy for the solid and a liquid?
Work out q by q= mc x change in temp
Then change in enthalpy per mole = q/n using the moles calculated earlier
What is the experiment for the enthalpy of combustion?
Add set volume of water to a beaker (add lid to reduce heat loss)
Vol = mass as water density is 1
Record initial temp in a table
Fix height of beaker above spirit burner
Burn alcohol for set time, record initial mass and change in mass and record the highest temp then calculate the change in temp
How to calculate the change in enthalpy per mole for a combustion?
Work out q (change in energy)
q = mc x change in temp
Calculate change in enthalpy per mole = q/n
Moles of alcohol = mass burned/Mr
What sign does delta H have for endothermic and exothermic reactions?
Endo = positive Exo = negative
What is the standard enthalpy of formation? (Check book for symbol)
This is the enthalpy change when 1 mole of a compound is formed from its elements with all reactants and products in standard states under standard conditions
What is the standard enthalpy of a reaction
This is the enthalpy change when substances react under standard conditions in quantities given by the equation for the reaction
What is the standard enthalpy of combustion?
This is the enthalpy change when 1 mole of a substance is burned completely in excess with all reactants in their standard states and under standard conditions
What are the standard conditions for w reactions?
298k and 100kPa
What is Hess’s law
Enthalpy change at constant pressure is independent of the route taken
