Calorimetry

Factors to Consider for Temperature change and why

• Mass -greater mass - more energy required to raise temperature

• Specific heat capacity - Greater specific heat capacity - more energy required to raise temperature

What us specific heat capacity

Energy required to raise the temperature of one gram of a substance by one Kelvin

Equation for Energy supplied/removed as heat and units

q=mcΔT

q= J m=mass=g c=Specific heat capacity=J/kg°C Temperature change = K

What is the process for the experiment of Flame Calorimetry

-Place beaker with known mass of water above flame

-Measure 1.Tempature change of water 2 ,Change in mass of the fuel

Analysis to find Enthalpy change in flame calorimetry

1) q=mcΔT

2) q= energy supplied to water so assume energy supplied to water= energy given out by combustion

3)divide by 1000 to get KJ

4)KJ / moles of fuel to get enthalpy change - add negative sign as exothermic

Explain experiment for coffee cup calorimetry

-Add known zinc to polystyrene cup to known mass of copper sulfate

let reaction proceed until zinc is udder up and record temperature change

Analysis for coffee up calorimetry

use mass of solution for q=mcΔT and repeat steps of flame calorimetry

How to work out mass with density and volume

Mass = Density / volume

What is Hess’ Law

Then enthalpy change of a reaction is the same independent of the route taken

What way arrows in Hess cycles in combustion

down

What way arrows in Hess cycles in Fromation

Up

2 ways to Manipulate data reaction equations

Change the direction of the arrow - Changes the sign of ΔH

Multiply all of the co-efficents by the same number - Multiplies the ΔH

Bond breaking is

Endothermic

Bond forming

Exothermic

What is Bond dissociation enthalpy

Enthalpy change when 1 mole of bond in a gaseous molecule is broken to give seperated atoms

What is mean bond enthalpy

Average bond for a particular type of bonds across a range of all molecules

Limitations of mean bond enthalpy

-Not 100% accurate as values taken are from a range of diffrent compounds

• less accurate for solid , liquids and solutions as they are based on gaseous