Measuring enthalpy change by experiment - DF

Question 1

How do we find enthalpy change through experiments

Answer 1

through change in temperature as enthalpy change cannot be measured directly

Question 2

2 different experiments to calculate enthalpy change

Answer 2

burning a fuel, reaction in a polystyrene cup

Question 3

Burning a fuel (enthalpy change experiment) method

Answer 3

set the apparatus so the sprit with the fuel is beneath the copper calorimeter with a specific mass of water being held by a boss and stand, the water should have a thermometer and draught shields. Take the initial temp of the specific mass of water and the initial mass of the spirit burner. Then heat up and take max final temp of water and finial mass of spirit burner. Then use E=mc(change in temp), then mole=mass/Mr and /1000

Question 4

Why does the burning a fuel (enthalpy change experiment) not give the perfect answer

Answer 4

heat loss to the surrounding
incomplete combustion
heat loss to the calorimeter
evaporation of the fuel

Question 5

Reaction in a polystyrene cup (enthalpy change experiment) method

Answer 5

take your acid and alkali and use pipettes so you know the volume of he solutions with known concentrations and place in 2 cups, take the starting temp of the 2 separate solutions. Then mix them into one polystyrene cup to minimise heat loss (exo) or heat gain (endo) and a lid. Stir the mixture and record the max (exo)/min (endo) temp reached. Then do E=mc(change in temp) but mass of solution after mixing instead of water and 4.18

Question 6

Reaction in a polystyrene cup (enthalpy change experiment) method but a solid instead of 2 liquids

Answer 6

if the reaction involves a solid reacting with the solution the procedure is similar but with 2 solutions the reaction happens instantly but with a solid it is slower meaning that you will have to take the temperature over a period of time to find the max temp. Then a graph of temp against time is plotted
https://mmerevise.co.uk/app/uploads/2022/10/Calorimmetry-Graph-e1666357024312.png

Question 7

ΔᵣH° meaning

Answer 7

standard enthalpy change of reaction - enthalpy change when molar quantities of the reactions as stated in the equation react together under standard conditions with all substances in their standard states

Question 8

Δ꜀H° meaning

Answer 8

standard enthalpy change of combustion - enthalpy change when 1 mole of the substance burns completely in oxygen under standard conditions with all substances in their standard states (always -)
https://www.chemistrylearner.com/wp-content/uploads/2022/10/Heat-of-Combustion.jpg

Question 9

ΔfH° meaning

Answer 9

standard enthalpy change of formation - enthalpy change when 1 mole of the substance is made from its elements in their standard states under standard conditions
https://www.chemguide.co.uk/physical/energetics/dhfwater.gif

Question 10

ΔₙₑᵤₜH°

Answer 10

standard enthalpy change of neutralisation - enthalpy change when 1 mole of H⁺ ions (from an aq acid), react with 1 mole of OH⁻ ions (from an aq alkali) to from one mole water under standard condition and in solution containing 1moddm^3 (always -)
https://images.squarespace-cdn.com/content/v1/5c5aed8434c4e20e953d6011/1624988877496-PEFQLR24MP5YB3FDJ6LB/neutralisation+ionic+equation.jpeg