University:
York University
Course:
CHEM 1001 | Chemical Dynamics
Academic year:

2022
Views:

73

Pages:

2
Author:

Niklas

First Law of Thermodynamics: ΔU = q + w = ΔE + PAV = ΔE + nRT Heat: Some of the added heat raises the temperature of the gas, and some does work on the surroundings. Molar Heat Capacity: Cv = (∂U/∂T)v for a monoatomic ideal gas Internal Energy: ΔU = qv + CvΔT = qv + nCvΔT Enthalpy: H = U + PV Enthalpy Change: ΔH = ΔU + PΔV = ΔU + nRΔT = CpΔT Heat Capacity of Polyatomic Gases: Have internal motions in addition to translations (vibrational and rotational modes) Larger Cv and Cp Cv and Cp are weakly T-dependent Heat Capacity of Solids and Liquids: Must be measured Heat: q = mCsΔT Hess's Law: The enthalpy change for an overall process is the sum of the individual enthalpy changes for each step. Enthalpy (ΔH): A state function, not affected by the steps taken Standard state: 1 atm pressure, 1 M concentration, 25°C (298.15 K) Enthalpy of formation (ΔHf): Heat given off when elements combine to form one mole of a compound Stability: More negative ΔHf is more stable, less negative is less stable Trends: Going down the periodic table, compounds become less stable. Going across the periodic table, they become more stable towards the middle and unstable to the right. Calorimetry: Coffee cup calorimetry: All heat is captured inside the system, constant pressure is observed, water is considered the surroundings. Potential energy (PE) increases when the physical state goes from solid to plasma. Bond breaking: Enthalpy is positive (BDE = bond dissociation energy). Spontaneity of Chemical Reactions: A spontaneous reaction proceeds in the forward direction under given conditions, regardless of the rate. Exothermic reactions are spontaneous most of the time. Work needs to be done on the surroundings for the reverse reaction when the forward reaction is exothermic. Expansion of a gas can be done reversibly (P_ext = P_int) or irreversibly (P_ext ≠ P_int). When temperature is constant, ΔE = q + w = 0.