General Chemistry Exam Study Guide: Chemical Kinetics, Equilibrium, Acid-Base Chemistry, and Laboratory Calculations

Chemical Kinetics

Rate Laws and Reaction Order

Chemical kinetics studies the speed of chemical reactions and the factors affecting them. The rate law expresses the relationship between the rate of a reaction and the concentration of reactants.

• Rate Law Definition: The rate law for a reaction is generally written as $\text{rate} = k[A]^m[B]^n$, where k is the rate constant, and m and n are the reaction orders with respect to reactants A and B.

• Determining Reaction Order: The reaction order is found experimentally by observing how changes in concentration affect the reaction rate.

• Example: For the reaction $N_2(g) + 3Cl_2(g) \rightarrow 2NCl_3(g)$, the rate law can be determined by analyzing initial rate data from multiple trials.

Experimental Determination of Rate Laws

Experimental data is used to deduce the rate law by comparing how the rate changes when reactant concentrations are varied.

• Method: Keep all but one reactant concentration constant and observe the change in rate.

• Example Table:

Trial	[N2]	[Cl2]	Rate (M/min)
I	0.200	0.300	0.100
II	0.200	0.600	0.200
III	0.400	0.300	0.200

• Analysis: Doubling [Cl2] doubles the rate, indicating first order in Cl2. Doubling [N2] also doubles the rate, indicating first order in N2.

Graphical Analysis in Kinetics

Graphs of concentration vs. time or absorbance vs. time are used to determine reaction order and rate constants.

• Zero Order: Linear decrease in concentration over time.

• First Order: Exponential decrease; linear when plotting ln[Reactant] vs. time.

• Second Order: Linear when plotting 1/[Reactant] vs. time.

• Example: Students use absorbance data to determine the order of reaction for Z by plotting different graphs and analyzing which is linear.

Acid-Base Chemistry

pH, pOH, and Acid/Base Strength

The pH scale measures the acidity of a solution, defined as $\text{pH} = -\log [H^+]$. The strength of acids and bases is quantified by their dissociation constants.

• pH Calculation: $\text{pH} = -\log [H^+]$

• pOH Calculation: $\text{pOH} = -\log [OH^-]$

• Relationship: $\text{pH} + \text{pOH} = 14$ (at 25°C)

• Acid Dissociation Constant (Ka): $K_a = \frac{[H^+][A^-]}{[HA]}$

• Base Dissociation Constant (Kb): $K_b = \frac{[OH^-][BH^+]}{[B]}$

• Percent Ionization: $\text{Percent Ionization} = \frac{[H^+]}{[HA]_{initial}} \times 100\%$

• Example: Calculating the pH and percent ionization of a weak acid solution.

Titration and Equivalence Point

Titration is a technique used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.

• Equivalence Point: The point at which the amount of titrant added is stoichiometrically equivalent to the amount of analyte in the sample.

• Calculation: Use the titration curve to determine the concentration of the unknown solution.

• Example: A titration curve of NaOH added to a weak acid shows the pH change and helps identify the equivalence point.

Chemical Equilibrium

ICE Tables and Equilibrium Calculations

An ICE table (Initial, Change, Equilibrium) is used to organize data and calculate equilibrium concentrations for reactions.

• Steps:

  1. List initial concentrations.

  2. Determine changes based on stoichiometry.

  3. Calculate equilibrium concentrations.

• Equilibrium Constant (K): $K = \frac{[\text{products}]}{[\text{reactants}]}$ at equilibrium.

• Example Table:

	Initial (M)	Change (M)	Equilibrium (M)
FeSCN2+	0	+x	x
Fe3+	0.0010	-x	0.0010-x
SCN-	0.0005	-x	0.0005-x

• Application: Use absorbance data and calibration curves to determine equilibrium concentrations and calculate K.

Laboratory Calculations and Safety

Concentration and Dilution Calculations

Calculating concentrations after mixing solutions or diluting stock solutions is a common laboratory task.

• Dilution Equation: $M_1V_1 = M_2V_2$

• Example: Mixing 100.0 mL of 0.100 M Fe(NO3)3 with 10.0 mL of 0.0200 M SCN- to prepare a standard solution.

Calibration Curves

Calibration curves relate absorbance to concentration and are used to determine unknown concentrations from spectrophotometric data.

• Beer-Lambert Law: $A = \varepsilon c l$

• Example: A calibration curve for FeSCN2+ is given by $A = 5521x + 0.043$, where x is concentration in M.

Safety in the Chemistry Laboratory

Proper safety procedures are essential when working with chemicals and glassware.

• Key Points:

  • Always wear safety goggles and appropriate clothing.

  • Do not eat or drink in the laboratory.

  • Never wear open-toed shoes or sandals.

  • Long hair should be tied back.

Reference Information

Periodic Table

The periodic table organizes elements by increasing atomic number and groups elements with similar chemical properties.

• Groups: Vertical columns (e.g., alkali metals, halogens, noble gases).

• Periods: Horizontal rows.

• Applications: Used to predict chemical behavior, electron configurations, and trends such as electronegativity and atomic radius.

Helpful Equations

• $A = -\log T$

• $A = \varepsilon c l$

• $\text{rate} = k[OH^-][CV^+]$

• $\text{rate} = k[CV^+][OH^-][CV^+]$

• $\text{rate} = k[OH^-][CV^+]$

• $\text{pH} = pK_a + \log \frac{[A^-]}{[HA]}$

Additional info: Some context and explanations have been expanded for clarity and completeness, including definitions and step-by-step methods for calculations.