CH40 – “H” is for “Henthalpy”

Dates

• P4 – Wednesday, April 25th
• P5 – Thursday, April 26th
• P7 – Friday, April 27th

Lab Recap

• what did you determine for “c” ?
• what identity did you determine for the metal?
• what factors introduced uncertainty?
• how might they have impacted the result?
• Q: what type of report would you like to submit?

New Idea – Enthalpy

• defined: H = E + PV
• not really meaningful
• useful definition: ΔH = Q_p
• enthalpy: think of this as the energy associated with a process
• enthalpy: think of this as “chemical energy” of formula
• reaction energy
• physical changes
• calorimetry
• H is a state function
• ΔH + means endothermic process
• ΔH – means exothermic process

Examples of Enthalpy

• ΔH_rxn = “heat” of a reaction
• ΔH_solv = “heat” of solvation
• ΔH_f = “heat” of formation
• ΔH_comb = “heat” of combustion

Enthalpy and Moles

• ΔH is a molar quantity related to quantity
• Example: Ch. 6 (42)

Enthalpy and Calorimetry

• reaction inside a caloriometer
• ΔH then confined inside
• ΔH –> Q inside calorimeter
• Example: Ch. 6 (62)

Homework

• Work on the lab report
• details agreed upon in class

Heads Up: Test Wed/Thu Next Week

• we did not test separately on acids and bases
• the next test will incorporate these ideas into the questions
• the course is slowly reaching convergence of all concepts from the first and second semester combined… THE CONVERGENCE IS COMING!