calorimetry
TRANSCRIPT
ENTHALPY CHANGESMeasuring and Expressing ∆H (Calorimetry)
OLEH :PUTRI ROSIDA R
8136141008
Introduction
We have been introduced to heat producing (exothermic) reactions and heat using (endothermic) reactions.
Introduction
We have been introduced to heat producing (exothermic) reactions and heat using (endothermic) reactions.
Heat is a measure of the transfer of energy from a system to the surroundings and from the surroundings to a system.
Introduction
We have been introduced to heat producing (exothermic) reactions and heat using (endothermic) reactions.
Heat is a measure of the transfer of energy from a system to the surroundings and from the surroundings to a system.
The change in heat of a system is called the change in enthalpy (ΔH) when the pressure of the system in kept constant.
Calorimetry
We measure the transfer of heat (at a constant pressure) by a technique called calorimetry.
In calorimetry ... the heat released by the system is
equal to the heat absorbed by its surroundings.
the heat absorbed by the system is equal to the heat released by its surroundings.
The total heat of the system and the surroundings remains constant.
Calorimetry
We use an insulated device called a calorimeter to measure this heat transfer.
A typical device is a “coffee cup calorimeter.”
Calorimetry
We use an insulated device called a calorimeter to measure this heat transfer.
A typical device is a “coffee cup calorimeter.”
Calorimetry
To measure ΔH for a reaction ...1.dissolve the reacting
chemicals in known volumes of water
2.measure the initial temperatures of the solutions
3.mix the solutions4.measure the final
temperature of the mixed solution
Calorimetry
The heat generated by the reactants is absorbed by the water.
We know the mass of the water, mwater.
We know the change in temperature, ∆Twater.
Calorimetry
The heat generated by the reactants is absorbed by the water.
We know the mass of the water, mwater.
We know the change in temperature, ∆Twater.
We also know that water has a specific heat of Cwater = 4.18 J/°C-g.
Calorimetry
The heat generated by the reactants is absorbed by the water.
We know the mass of the water, mwater.
We know the change in temperature, ∆Twater.
We also know that water has a specific heat of Cwater = 4.18 J/°C-g.
We can calculate the heat of reaction by:
Calorimetry
The heat generated by the reactants is absorbed by the water.
We know the mass of the water, mwater.
We know the change in temperature, ∆Twater.
We also know that water has a specific heat of Cwater = 4.18 J/°C-g.
We can calculate the heat of reaction by:
qsys = ∆H = −qsurr = -mwater × Cwater × ∆Twater
Example
When 25.0 mL of water containing 0.025 mol of HCl at 25.0°C is added to 25.0 mL of water containing 0.025 mol of NaOH at 25.0°C in a coffee cup calorimeter, a reaction occurs. Calculate ∆H (in kJ) during this reaction if the highest temperature observed is 32.0°C. Assume the densities of the solutions are 1.00 g/mL.Knowns: Vfinal = VHCl + VNaOH = (25.0 + 25.0) mL = 50.0 mL Dwater = 1.00 g/mL ∆Twater = Tfinal − Tinitial = 32.0°C − 25.0°C = +7.0°C Cwater = 4.18 J/°C-gCalculation: mwater = 50.0 g
∆H = −1463 J = −1.5×103 J = −1.5 kJ
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”• A sample is placed in the crucible.
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”• Oxygen is introduced into the chamber.
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”• The lid is tightened and the chamber is placed in a water bath.
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”• The ignition coil ignites the sample.
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”• The heat generated in the chamber is transferred to the water.
Calorimetry
We can also do calorimetry at a constant volume rather than at a constant pressure.
This is called “bomb calorimetry.”• The change in temperature is then measured on the thermometer.
Summary
Heat is a measure of the transfer of energy from a system to the surroundings and from the surroundings to a system.
The change in heat of a system is called the change in enthalpy (ΔH) when the pressure of the system in kept constant.
We measure the transfer of heat (at a constant pressure) by a technique called calorimetry.
We use an insulated device called a calorimeter to measure this heat transfer.
Summary
Two calorimeters used are ... the coffee cup calorimeter (for
constant pressure measurements) the bomb calorimeter (for constant
volume measurements)