Calorimetric Equations II and

Delicious ApplicationsPutting it Together

CalorimetryWhat is Calorimetry?What is a Calorimeter?

Three Assumptions of Simple Calorimeters:

1. No heat is transferred between the calorimeter and the outside environment

2. Any heat absorbed or released by the calorimeter materials, such as the container, is negligible

3. A dilute aqueous solution is assumed to have a density and specific heat capacity equal to that of pure water (1.00g/ml and 4.184 J/g°C)

SolutionCombustionNeutralization(Vaporization)

Remember what we’ve seen

ΔH = nΔHx

ΔHsystem = ±|qsurroundings|

q = mcΔT

n = m/MM n = C x V

Doing Calorimetric problems is about using

these equationsΔH = nΔHx ΔHsystem = ±|qsurroundings|

nΔHx = qsurroundings

nΔHx = mcΔTn = mcΔT / ΔHx

m/MM = mcΔT / ΔHx

Calorimetry of SolutionOne substance dissolves in

another

NaBr(s) Na+(aq) + Br-

(aq)

Heat of Solution Demohttp://www.teachersdomain.org/resource/lsps07.

sci.phys.matter.dissolvesalt/

Calorimetry of CombustionBurn a substance in oxygen to

yield CO2 and H2O

C3H8(l) + 5O2(g) 3CO2(g) + 4H2O(l)

Question 3 If the molar enthalpy of

combustion of propane is -2220KJ/mol, what mass of propane will have to be burned in order to raise the temperature of 1.00L of water from 50.0 to 85°C.

Question 4A calorimeter (C=0.850J/˚C)

containing 5.00 x 102 ml of water at 22 oC is warmed to 100oC when 9.00 g of cheddar cheese is burned. Calculate the heat absorbed by the water and the heat of combustion, per gram, of cheese.

Calorimetry of NeutralizationAcid + Base Salt + Water

HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)

Use the same strategy for other reactions

CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)

Neutralization demo50ml of 1 mol/L HCl (strong acid)50ml of 1 mol/L NaOH (strong base)

HCl + NaOH NaCl + H2O

Question 5A chemist wanted to find the heat of

neutralization of HCl with NaOH. She added 61.1ml of 0.543M HCl to 42.6ml of 0.779M NaOH. The initial temperature of both solutions was 17.8oC and the highest recorded temperature of the solution after neutralization was 21.6˚C. What is the enthalpy of neutralization of HCl?

ASSUME: The density and heat capacity of the solutions is the same as that for pure water

Question 650.0 mL of 0.300 mol/L CuSO4 solution is mixed

with an equal volume of 0.600 mol/L NaOH. The initial temperature of both solutions is 21.4oC. After mixing the solutions in the coffee-cup calorimeter, the highest temperature that is reached is 24.6oC. Determine the enthalpy change of the reaction.

CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)

But wait, there’s more…Heat of Vaporization H2O(l) + ∆H H2O(g)

How a fridge works

Heats of VaporizationFreon – qvap 232kj/kg

Water – qvap 2257 kj/kg

Propane – qvap428 kj/kg

Ammonia – qvap 1369 kj/kg

Ethyl Alcohol – qvap 846 kj/kg

So Why Use FreonUnreactiveChemically SafeHigh qvap

Boiling point below target temp

WHY NOT? ChlorofluorocarbonBAD FOR THE ENVIRONMENT!!!!

Making Ice Cream

Who knew thermochemistry could taste so good?

Ingredients(½ cup) 125ml Milk (we’re using 2%)(½ cup) 125ml Cream (we’re using 35%)(¼ cup) 67.5g Sugar(¼ tsp) ~1ml Vanilla Extract/flavouringFor the bag:(½ to 1 cup) 250g Sodium Chloride(2 cups) 500g ice

Heat of SolutionWhy are we adding salt?What does salt do to the melting point/freezing

point of ice/water?Why not just use ice?Why not use a more endothermic substance i.e.

NH3NO3?Why do we salt our roads?

Recipe…I mean…ProcedureAdd ingredients to small bagCLOSE IT TIGHTLY (push out most of the air)Put the small bag in the big bagAdd ice and salt to the big bagCLOSE IT TIGHTLY Swish the big bag back and forthCaution: it will get really cold (duh…but seriously, its

colder than you’d think)

Mr. Sheps Ice Cream Attempts

Which one has sugar? Which one has a higher fat content?

Let’s Make Ice Cream