Hello future chemistry master! It's fantastic you're getting a head start on your exam preparation. Applied Chemistry concepts are all about connecting theory to real-world scenarios, and practice is key. Let's get you squared away with a concise review and then a stimulating quiz to test your readiness. You've got this!
Quick Study Guide: Applied Chemistry Essentials
- Stoichiometry & Yield:
- Mole Concept: The central unit for relating mass, moles, and number of particles. Use molar mass to convert between grams and moles.
- Limiting Reactant: The reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can be formed.
- Percent Yield: A measure of the efficiency of a reaction, calculated as $Percent\ Yield = \frac{Actual\ Yield}{Theoretical\ Yield} \times 100\%$.
- Acid-Base Chemistry:
- pH Scale: Measures the acidity or basicity of an aqueous solution. $pH = -log[H^+]$.
- Neutralization: Reaction between an acid and a base, typically forming water and a salt. For strong acid-strong base, $M_aV_a = M_bV_b$ at equivalence.
- Chemical Equilibrium:
- Equilibrium Constant ($K_c, K_p$): Relates the concentrations (or partial pressures) of products to reactants at equilibrium. $K_c = \frac{[Products]^{coefficients}}{[Reactants]^{coefficients}}$ (for $aA + bB \rightleftharpoons cC + dD$, $K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}$).
- Le Chatelier's Principle: A system at equilibrium, when subjected to a stress, will adjust itself to counteract the stress and re-establish a new equilibrium. Stresses include changes in concentration, temperature, and pressure (for gases).
- Thermochemistry:
- Enthalpy Change ($\Delta H$): Heat absorbed or released during a chemical reaction at constant pressure. Positive $\Delta H$ is endothermic, negative $\Delta H$ is exothermic.
- Heat Calculation: $q = mc\Delta T$ (where $q$ is heat, $m$ is mass, $c$ is specific heat capacity, and $\Delta T$ is change in temperature).
- Electrochemistry:
- Redox Reactions: Involve the transfer of electrons. Oxidation is loss of electrons (increase in oxidation number), reduction is gain of electrons (decrease in oxidation number).
- Standard Cell Potential ($E^\circ_{cell}$): The potential difference between two half-cells under standard conditions. $E^\circ_{cell} = E^\circ_{reduction} - E^\circ_{oxidation}$.
- Gibbs Free Energy & Cell Potential: $\Delta G^\circ = -nFE^\circ_{cell}$ (where $n$ is moles of electrons, $F$ is Faraday's constant: $96485\ C/mol$).
Practice Quiz
-
Question 1:
In the reaction $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$, if 4 moles of $H_2$ react with 1 mole of $O_2$, which reactant is limiting?
- $H_2$
- $O_2$
- Neither, both are consumed completely.
- The reaction cannot occur with these amounts.
-
Question 2:
A solution has a hydrogen ion concentration of $[H^+] = 1.0 \times 10^{-4}\ M$. What is its pH?
- 10
- 7
- 4
- -4
-
Question 3:
Consider the reversible reaction: $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) + \text{heat}$.
According to Le Chatelier's Principle, what effect will increasing the temperature have on the equilibrium?
- Shift to the right, favoring product formation.
- Shift to the left, favoring reactant formation.
- No effect on the equilibrium position.
- Increase the equilibrium constant ($K_c$).
-
Question 4:
If 50.0 g of water at $25.0^\circ C$ absorbs 4180 J of heat, what will be its final temperature? (Specific heat capacity of water, $c = 4.18\ J/g^\circ C$)
- $15.0^\circ C$
- $25.0^\circ C$
- $45.0^\circ C$
- $50.0^\circ C$
-
Question 5:
Which of the following processes represents an oxidation reaction?
- $Cl_2 \rightarrow 2Cl^-$
- $Fe^{3+} \rightarrow Fe^{2+}$
- $Zn \rightarrow Zn^{2+}$
- $Cr_2O_7^{2-} \rightarrow Cr^{3+}$
-
Question 6:
You have a 2.0 M stock solution of HCl. How much of this stock solution do you need to prepare 500 mL of a 0.50 M HCl solution?
- 100 mL
- 125 mL
- 200 mL
- 250 mL
-
Question 7:
Which functional group is characteristic of an ester?
- $-\text{COOH}$
- $-\text{OH}$
- $-\text{CHO}$
- $-\text{COO}\text{R'}$
Click to see Answers
- Question 1: B. $O_2$
Explanation: From the stoichiometry, 2 moles of $H_2$ react with 1 mole of $O_2$. If you have 4 moles of $H_2$, it would require 2 moles of $O_2$. Since only 1 mole of $O_2$ is available, $O_2$ is the limiting reactant.
- Question 2: C. 4
Explanation: $pH = -log[H^+] = -log(1.0 \times 10^{-4}) = 4$.
- Question 3: B. Shift to the left, favoring reactant formation.
Explanation: The reaction is exothermic (releases heat). Increasing temperature is like adding a product (heat), so the equilibrium will shift to consume the added heat, moving in the reverse (endothermic) direction, favoring the reactants.
- Question 4: C. $45.0^\circ C$
Explanation: $q = mc\Delta T \implies \Delta T = \frac{q}{mc} = \frac{4180\ J}{(50.0\ g)(4.18\ J/g^\circ C)} = \frac{4180}{209} = 20^\circ C$. Final temperature = Initial temperature + $\Delta T = 25.0^\circ C + 20^\circ C = 45.0^\circ C$.
- Question 5: C. $Zn \rightarrow Zn^{2+}$
Explanation: Oxidation is the loss of electrons, resulting in an increase in oxidation number.
A) $Cl_2 \rightarrow 2Cl^-$ (0 to -1, reduction)
B) $Fe^{3+} \rightarrow Fe^{2+}$ (+3 to +2, reduction)
C) $Zn \rightarrow Zn^{2+}$ (0 to +2, oxidation)
D) $Cr_2O_7^{2-} \rightarrow Cr^{3+}$ (Cr goes from +6 to +3, reduction)
- Question 6: B. 125 mL
Explanation: Use the dilution formula: $M_1V_1 = M_2V_2$.
$(2.0\ M)(V_1) = (0.50\ M)(500\ mL)$
$V_1 = \frac{(0.50\ M)(500\ mL)}{2.0\ M} = \frac{250\ mL}{2.0} = 125\ mL$.
- Question 7: D. $-\text{COO}\text{R}'$
Explanation:
A) $-\text{COOH}$ is a carboxylic acid.
B) $-\text{OH}$ is an alcohol (or hydroxyl group).
C) $-\text{CHO}$ is an aldehyde.
D) $-\text{COO}\text{R}'$ represents an ester linkage (where R' is another alkyl or aryl group).