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General Chemistry Exam - Cheatsheet

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Section 1

General Chemistry Exam - Cheatsheet

STUDY GUIDE

๐ŸŽ“ General Chemistry Exam - Study Guide

๐Ÿ“‹ Course Structure

code
๐Ÿ“š General Chemistry
โ”œโ”€โ”€ ๐Ÿ“– Chapter 1: The Dynamics of Chemical Equilibrium
โ”œโ”€โ”€ ๐Ÿ“– Chapter 2: Writing Equilibrium Constant Expressions; Relationships between Kษ› and Kp Values
โ”œโ”€โ”€ ๐Ÿ“– Chapter 3: Manipulating Equilibrium Constant Expressions
โ”œโ”€โ”€ ๐Ÿ“– Chapter 4: Equilibrium Constants and Reaction Quotients
โ”œโ”€โ”€ ๐Ÿ“– Chapter 5: Heterogeneous Equilibria
โ”œโ”€โ”€ ๐Ÿ“– Chapter 6: Le Chรขtelier's Principle
โ”œโ”€โ”€ ๐Ÿ“– Chapter 7: Calculations Based on K
โ”œโ”€โ”€ ๐Ÿ“– Chapter 8: Equilibrium and Thermodynamics
โ””โ”€โ”€ ๐Ÿ“– Chapter 9: Changing K with Changing Temperature
Section 2

๐Ÿ“– Chapter 1: The Dynamics of Chemical Equilibrium

What this chapter covers: This chapter introduces the fundamental concepts of chemical equilibrium, including the conditions necessary for equilibrium, the relationship between forward and reverse reaction rates, and the meaning of the equilibrium constant. It sets the stage for understanding more complex equilibrium calculations and applications.

๐Ÿ”‘ Essential Concepts & Formulas

Concept/FormulaDefinition/EquationWhen to Use
Chemical EquilibriumDynamic state where forward and reverse rates are equal.Understanding reaction completion.
Reversible ReactionReaction that can proceed in both directions.Achieving chemical equilibrium.
Equilibrium Constant (K)Ratio of product to reactant concentrations at equilibrium.Quantifying equilibrium position.
K and Rate ConstantsK=kf/krK = k_f / k_rRelating rate constants to equilibrium.

๐Ÿ› ๏ธ Problem Types

Type A: Determining Equilibrium Conditions

Setup: "Given a reaction, identify if it can reach equilibrium."

Method: Check if the reaction is reversible and if the rates of forward and reverse reactions are equal.

Type B: Calculating K from Rate Constants

Setup: "Given forward and reverse rate constants, calculate K."

Method: Use the formula K=kf/krK = k_f / k_r.

๐Ÿงฎ Solved Example

Problem: The forward rate constant for a reaction is 1.50ร—10โˆ’2sโˆ’11.50 \times 10^{-2} s^{-1} and the reverse rate constant is 4.50ร—10โˆ’2sโˆ’14.50 \times 10^{-2} s^{-1}. Calculate the equilibrium constant K.

Given: kf=1.50ร—10โˆ’2sโˆ’1k_f = 1.50 \times 10^{-2} s^{-1}, kr=4.50ร—10โˆ’2sโˆ’1k_r = 4.50 \times 10^{-2} s^{-1}

Steps:

  1. Identify the formula: K=kf/krK = k_f / k_r
  2. Substitute the values: K=(1.50ร—10โˆ’2)/(4.50ร—10โˆ’2)K = (1.50 \times 10^{-2}) / (4.50 \times 10^{-2})
  3. Calculate: K=0.333K = 0.333
"
โœ…
Answer: K=0.333K = 0.333

โš ๏ธ Common Mistakes

โŒ Mistake: Assuming equal reactant and product concentrations at equilibrium.

โœ… How to avoid: Remember equilibrium is about equal rates, not necessarily equal concentrations.

๐Ÿ“– Chapter 2: Writing Equilibrium Constant Expressions; Relationships between Kษ› and Kp Values

What this chapter covers: This chapter focuses on writing correct equilibrium constant expressions for both homogeneous and heterogeneous reactions. It also explores the relationship between Kc (equilibrium constant in terms of concentrations) and Kp (equilibrium constant in terms of partial pressures).

๐Ÿ”‘ Essential Concepts & Formulas

Concept/FormulaDefinition/EquationWhen to Use
KcEquilibrium constant in terms of molar concentrations.Calculating equilibrium with concentrations.
KpEquilibrium constant in terms of partial pressures.Calculating equilibrium with partial pressures.
Relationship between Kc and KpKp=Kc(RT)ฮ”nKp = Kc(RT)^{\Delta n}Converting between Kc and Kp.
ฮ”nChange in the number of moles of gas.Determining if Kp = Kc.

๐Ÿ› ๏ธ Problem Types

Type A: Writing Kc and Kp Expressions

Setup: "Given a balanced chemical equation, write the Kc or Kp expression."

Method: Use the stoichiometric coefficients as exponents and place products over reactants.

Type B: Converting between Kc and Kp

Setup: "Given Kc, temperature, and ฮ”n, calculate Kp."

Method: Use the formula Kp=Kc(RT)ฮ”nKp = Kc(RT)^{\Delta n}.

๐Ÿงฎ Solved Example

Problem: For the reaction N2(g)+3H2(g)โ‡Œ2NH3(g)N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g), Kc=0.50Kc = 0.50 at 400 K. Calculate Kp.

Given: Kc=0.50Kc = 0.50, T=400KT = 400 K, ฮ”n=2โˆ’(1+3)=โˆ’2\Delta n = 2 - (1+3) = -2

Steps:

  1. Identify the formula: Kp=Kc(RT)ฮ”nKp = Kc(RT)^{\Delta n}
  2. Substitute the values: Kp=0.50ร—(0.0821ร—400)โˆ’2Kp = 0.50 \times (0.0821 \times 400)^{-2}
  3. Calculate: Kp=0.50ร—(32.84)โˆ’2=0.000464Kp = 0.50 \times (32.84)^{-2} = 0.000464
"
โœ…
Answer: Kp=0.000464Kp = 0.000464

โš ๏ธ Common Mistakes

โŒ Mistake: Incorrectly calculating ฮ”n.

โœ… How to avoid: Ensure you subtract the sum of reactant coefficients from the sum of product coefficients.

๐Ÿ“– Chapter 3: Manipulating Equilibrium Constant Expressions

What this chapter covers: This chapter explains how the value of the equilibrium constant changes when the chemical equation is manipulated (e.g., reversed, multiplied by a factor). Understanding these manipulations is crucial for relating different equilibrium constants to each other.

๐Ÿ”‘ Essential Concepts & Formulas

Concept/FormulaDefinition/EquationWhen to Use
Reversing a ReactionKโ€ฒ=1/KK' = 1/KCalculating K for the reverse reaction.
Multiplying by a Factor (n)Kโ€ฒ=KnK' = K^nCalculating K when scaling coefficients.
Combining ReactionsKtotal=K1ร—K2K_{total} = K_1 \times K_2Calculating K for a series of reactions.

๐Ÿ› ๏ธ Problem Types

Type A: Calculating K for a Reversed Reaction

Setup: "Given K for a forward reaction, find K for the reverse reaction."

Method: Take the inverse of the original K.

Type B: Calculating K after Scaling Coefficients

Setup: "Given K for a reaction, find K if the coefficients are multiplied by n."

Method: Raise the original K to the power of n.

๐Ÿงฎ Solved Example

Problem: For the reaction N2O4(g)โ‡Œ2NO2(g)N_2O_4(g) \rightleftharpoons 2NO_2(g), K=0.14K = 0.14 at 25ยฐC. What is K for the reaction 2NO2(g)โ‡ŒN2O4(g)2NO_2(g) \rightleftharpoons N_2O_4(g)?

Given: K=0.14K = 0.14 for N2O4(g)โ‡Œ2NO2(g)N_2O_4(g) \rightleftharpoons 2NO_2(g)

Steps:

  1. Identify the formula: Kโ€ฒ=1/KK' = 1/K
  2. Substitute the value: Kโ€ฒ=1/0.14K' = 1/0.14
  3. Calculate: Kโ€ฒ=7.14K' = 7.14
"
โœ…
Answer: Kโ€ฒ=7.14K' = 7.14

โš ๏ธ Common Mistakes

โŒ Mistake: Forgetting to invert K when reversing a reaction.

โœ… How to avoid: Always remember to take the reciprocal of K for the reverse reaction.

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