CHE 132 Midterm 1 Review Aminov PDF

Preview

Summary

Powerpoint Presentation from Undergrad TA-led review for midterm 1 Spring 2019. Also see pdf with worked out solutions...

Description

CHE 132: MIDTERM 1 REVIEW Jonathan Aminov and Ali Ahmadi

Thermodynamics • First Law of Thermodynamics: Energy of the universe is constant • Universe = System + Surroundings

• Internal Energy is the energy in the system (IE change = ΔE)

• q = heat • w = work

IE, Heat, and Work Questions 1. A chemical reaction is run in which 590 Joules of heat are generated and 888 Joules of work are done on the system. Calculate the change in internal energy of the system.

Continued 1.

Calculate the change in internal energy (ΔE) for a system which transfers 400 J of heat to the surroundings in an exothermic process in which 250 J of work are done on the system.

Practice Question

Enthalpy ● ● ●

Enthalpy is a state function - a property whose value does not depend on the path taken to reach the specific value ΔH = ΔE + PΔV ΔH = q only during constant pressure

Entropy ●

●

Entropy determines if the reaction will go or not Spontaneous Process: A process that occurs without an external energy cost ○

●

Nonspontaneous Process: Requires energy from an external source ○

●

Ex: Ball rolling down a hill

Ex: Ball rolling up a hill

Spontaneity ≠ Enthalpy

Entropy (S)

Entropy increases as we go from solid to liquid to gas

Entropy (S) ●

● ● ● ●

S = Entropy W = # of available configurations (microstates) kB = Boltzmann Constant = 1.3806 x 10-23 J/K J/K are entropy units S cannot be negative but ΔS can be

Practice Question - Configurational Entropy 1. What is W for 2 Xe atoms with 14 binding sites? a. b.

Must account for “double counting” by dividing by 2 If the number of atoms is greater than 2, then divide by the factorial of the number of atoms in order to account for multiple counting

Configurational Entropy Continued 1. What is W for 2 atoms (1 Xe, 1 Ne) for 14 binding sites? a.

In this case, we do not need to account for “multiple counting” because we want to include the possibilities of alternating the atoms that start since these are no longer indistinguishable.

Configurational Entropy Practice Exam Q.

Entropy-Enthalpy Relationship ●

When pressure and temperature are constant, qrev = ΔH

Enthalpy-Entropy Relationship Exam Q.

C3H8 Molar Mass: 44.1 g/mol

Gibbs Free Energy •

Free energy determines the driving force of a chemical process

ΔG = ΔH-TΔS MUST KNOWS: ● NEGATIVE ΔG = SPONTANEOUS Reaction ● POSITIVE ΔG = NON spontaneous Reaction ● ΔG = 0 Reaction is in equilibrium and BOTH reverse and forward reactions are equal (No driving force) ○

This means the reaction is reversible

Gibbs Free Energy -

ie.

Delta G of Formation for compounds in their standard state is 0

Formulas to Convert

Knowledge Check

C7H16 Molar Mass: 100.21 g/mol

Equilibrium Reactions are not one way. There is a forward and reverse and is denoted by the double head arrow.

Forward reactions: Reactants → Products Reverse Reactions: Products → Reactants At Equilibrium: Forward and Reverse reactions are EQUAL! This means that the concentration of the reactants and products are not changing.

Equilibrium of Reactions

Molar Masses (g/mol): TiCl4 (l) = 189.679 Ti (s) = 47.867 Cl2 (g) 70.906

Reaction Quotient, Q Used for reactions not in equilibrium

Le Chatelier’s Principle ●

●

If a reaction is stressed, it tends to shift to the direction that relieves the stress Reactants↑ then Products↑ to “compensate” for the stress ○

● ●

Removing product causes more products to form Treat heat as a product ○ ○

●

●

The same is true for the reverse

Endothermic = Heat on reactants side Exothermic = Heat on products side

Pressure increase (volume decrease) = Shift towards side with fewer moles Pressure decrease (volume increase) = Shift towards side with more moles

Equilibrium Calculations - ICE Tables Initial = I 2. Change = C 3. Equilibrium = E 4. Solved = S (at the end) Always make sure to write out the equilibrium constant expression 1.

Equilibrium and Free Energy...