1. Calorimetry Remember… Heat lost by system = Heat absorbed by surroundings

2. Chemical/physical changes in the lab are open to atmosphere, so the changes occur at a constant pressure
Heat content of a system at constant pressure is called enthalpy, H
Heat released or absorbed by system at constant pressure is the change in enthalpy, (∆H)

3. The reactions we look at are at constant pressure so q = ∆H
∆H is positive = ___________
∆H is negative = ___________
qsys = ∆H = -qsurr = - m x C x ∆T

4. When 25 mL of water containing mol HCl at 25.0°C is added to 25.0 mL of water containing mol NaOH at 25.0°C in a foam cup calorimeter, a reaction occurs. Calculate the enthalpy change 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.

5. Thermochemical Equations Show enthalpy change in the reaction
CaO + H2O  Ca(OH)2 + heat
In a chem. rxn. ∆H for the rxn. can be written as product or reactant
2NaHCO  Na2CO3 + H2O + CO2
**absorbs 129 kJ of heat

6. The enthalpy change for the chemical equation exactly as it’s written
Heat of Reaction
The enthalpy change for the chemical equation exactly as it’s written
As ∆H (heat flow at constant pressure)
q, + /-
CaO H2O  Ca(OH) k J

8. Calculating Enthalpy Changes in a Reaction
2NaHCO kJ  Na2CO3 + H2O + CO2
What do we know from the equation?

9. 2NaHCO kJ  Na2CO3 + H2O + CO2
How much heat would be needed to decompose 2.24 mol NaHCO3?
How much heat would be absorbed in decomposing 9.0 g of NaHCO3?

10. If a piece of gold (C = 0. 129 J/g°C) with a mass of 45
If a piece of gold (C = J/g°C) with a mass of 45.5 g and a temperature of 80.5°C is dropped into 192 g of water at 15.0°C, what is the final temperature of the system?