Chemistry Concepts Overview
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Questions and Answers

What is the pH of the solution after 50.0 mL of NaOH was added to a 200.0 mL solution of 0.40 M ammonium chloride?

  • 9.25 (correct)
  • 4.75
  • 5.02
  • 8.98

What is the oxidation number of chromium in ammonium dichromate, (NH4)2Cr2O7?

  • +4
  • +6 (correct)
  • +3
  • +5

Which statement accurately describes reduction in a chemical context?

  • Gain of protons
  • Loss of mass
  • Gain of electrons (correct)
  • Loss of electrons

Which cell diagram accurately represents the voltaic cell generated by the reaction of zinc with lead ions?

<p>Zn(s) | Zn2+(aq) || Pb2+(aq) | Pb(s) (D)</p> Signup and view all the answers

In the construction of a voltaic cell with Ag(CN)2- and Cr, which of the following cell diagrams is correct?

<p>Ag(CN)2-(aq) | Ag(s) || Cr(s) | Cr3+(aq) (D)</p> Signup and view all the answers

Which half-reaction indicates that Pb is a stronger oxidizing agent than Au?

<p>Pb + 2 e- Pb2+ (A)</p> Signup and view all the answers

Which of the following species can act as a better reducing agent than Al?

<p>K+ (C)</p> Signup and view all the answers

Which statement is correct based on the half-reactions provided?

<p>Mg will oxidize I2. (C)</p> Signup and view all the answers

Which half-reaction shows a species that can be readily reduced?

<p>Au3+ + 3 e- Au (D)</p> Signup and view all the answers

Which of the following species is a better oxidizing agent than I2?

<p>Br2 (C)</p> Signup and view all the answers

Which sodium salt solution will exhibit the highest pH and therefore be the most basic?

<p>NaD (D)</p> Signup and view all the answers

What is the pH of coffee with a hydroxide ion concentration of $1 imes 10^{-10}$ M?

<p>4.0 (D)</p> Signup and view all the answers

What is the hydronium ion concentration of a $0.010$ M acetic acid solution?

<p>$4.2 imes 10^{-4}$ (B)</p> Signup and view all the answers

What is the concentration of [OH–] in a $0.20$ M ammonia solution?

<p>$1.9 imes 10^{-3}$ M (B)</p> Signup and view all the answers

Which expression can be used to calculate the hydronium ion concentration for weak acids with small Ka values?

<p>[H+] = (Ka [HA])^{1/2} (D)</p> Signup and view all the answers

Which salt forms an aqueous solution with a pH = 7?

<p>NaBr (A)</p> Signup and view all the answers

What mole ratio of Na2HPO4/NaH2PO4 is necessary to produce a buffer solution with a pH of 7.4?

<p>1.6 (D)</p> Signup and view all the answers

What relationship holds at the halfway point to the equivalence point in a titration curve of a weak acid with a strong base?

<p>The pH is equal to the pKa. (D)</p> Signup and view all the answers

What is defined as the energy transferred due to a temperature difference?

<p>Heat (B)</p> Signup and view all the answers

If ΔSsys is negative during a spontaneous chemical reaction, what does this imply about ΔSsurr?

<p>ΔSsurr is greater than 0 and its magnitude is greater than ΔSsys. (C)</p> Signup and view all the answers

What can be inferred about the entropy change when sodium hydroxide dissolves in water, resulting in a temperature rise?

<p>ΔSsys is greater than 0 and ΔSsurr is greater than 0. (B)</p> Signup and view all the answers

Which of the following statements about reaction rates and kinetic molecular theory is false?

<p>Collisions between product molecules do not impact overall reaction rates. (D)</p> Signup and view all the answers

What is the nature of the steps that make up a reaction mechanism?

<p>Elementary steps (B)</p> Signup and view all the answers

In a proposed mechanism for ozone decomposition, which species is classified as an intermediate?

<p>ClO (A)</p> Signup and view all the answers

What is likely to happen to the reaction rate as the concentration of reactants decreases over time?

<p>The reaction rate will decrease. (C)</p> Signup and view all the answers

What does it mean if the entropy change of the system is greater than zero?

<p>The overall process may still be spontaneous. (C)</p> Signup and view all the answers

What is the value of $ riangle G^{ heta}$ for the reaction forming ammonia at 298 K?

<p>-33.32 kJ/mol (C)</p> Signup and view all the answers

What is the overall order of the reaction 2 NO(g) + Cl2(g) → 2 NOCl(g) based on experimental data?

<p>3 (D)</p> Signup and view all the answers

What is the half-life of a first-order reaction with a rate constant of 3.45 x 10^-3 s^-1?

<p>200 s (C)</p> Signup and view all the answers

In the acid-base reaction CH3NH2 + HSO4– ⇄ CH3NH3+ + SO42–, identify the acid reactant.

<p>HSO4– (A)</p> Signup and view all the answers

What is the pH of a buffer solution where [HA] = [A–]?

<p>pKa (B)</p> Signup and view all the answers

What is the rate of reaction of nitrogen monoxide and hydrogen in mols/s?

<p>$7.01 \times 10^{-5}$ (D)</p> Signup and view all the answers

Which reaction path indicates the effect of a catalyst?

<p>Dotted line (A)</p> Signup and view all the answers

What is the value of Ecell for a concentration cell with silver electrodes at 0.10 M and 0.00003 M silver nitrate?

<p>+0.21 V (B)</p> Signup and view all the answers

How many seconds does it take for the concentration of formic acid to decrease by 87.5%?

<p>4.6 s (D)</p> Signup and view all the answers

Determine the rate expression for the reaction A + B → C based on the provided initial rate data.

<p>Rate = 24[A][B]^2 (B)</p> Signup and view all the answers

Which reaction pathway shows the effect of a catalyst on an uncatalyzed reaction?

<p>Pathway B (B)</p> Signup and view all the answers

What is the rate constant for a second-order reaction if the concentration decreases from 1.00 M to 0.43 M in 75 seconds?

<p>$1.8 \times 10^{-2}$ L/mol⋅s (B)</p> Signup and view all the answers

What happens to concentrations at equilibrium when K >> 1?

<p>The concentrations of products drastically increase. (B)</p> Signup and view all the answers

Which statement is true regarding the concentration of products at equilibrium?

<p>They remain constant as forward and reverse rates are equal. (B)</p> Signup and view all the answers

What must be true if the forward and reverse rate constants are unequal?

<p>The rates will remain unequal despite concentration changes. (B)</p> Signup and view all the answers

What is the effect of an increase in temperature on the equilibrium constant K?

<p>It depends on the enthalpy change of the reaction. (D)</p> Signup and view all the answers

Flashcards

Energy transferred due to temperature difference

Heat is the energy transferred between objects due to a temperature difference.

Spontaneous reaction with ΔSsys < 0

If the system's entropy decreases (ΔSsys < 0) during a spontaneous reaction, the surroundings' entropy must increase (ΔSsurr > 0) to compensate and make the overall entropy change positive.

NaOH dissolving in water

When NaOH dissolves in water, the system's entropy increases (ΔSsys > 0) because the ions become more dispersed. The increase in temperature means heat is released to the surroundings (ΔSsurr > 0).

Reaction rate and concentration

Higher reactant concentrations lead to more collisions and faster reactions. More collisions lead to a greater chance of a reaction.

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Reaction mechanism

A sequence of elementary steps that describe how a reaction occurs.

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Reaction intermediate

A species that is formed in one step of a reaction mechanism and consumed in a later step, but is not a final product.

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Elementary step

An elementary step is a single molecular event in a reaction mechanism.

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Reaction rate and reactants

As a reaction progresses, the concentration of reactants decreases causing the reaction rate to decrease.

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pH of coffee

A cup of coffee with a hydroxide ion concentration of 1 x 10⁻¹⁰ M has a pH of 4.

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Hydronium ion concentration of acetic acid

A 0.010 M solution of acetic acid has a hydronium ion concentration of 1.8 x 10⁻⁴ M.

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Ammonia solution concentration

The hydroxide ion concentration in a 0.20 M ammonia solution is 3.6 x 10⁻⁶ M.

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Weak acid hydronium ion calculation

When Ka values are small and concentrations of weak acids [HA] are relatively large, the hydronium ion concentration can be calculated using [H+] = √(Ka[HA])

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pH of salt solution

NaBr forms aqueous solutions with pH = 7.

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Buffer solution pH calculation

A buffer solution with 0.600 M lactic acid (HC₃H₅O₃)and 0.620 M lactate ion (C₃H₅O₃⁻) and the addition of 0.100 M potassium hydroxide to 0.5 L has a pH of 3.90

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Sodium phosphate mole ratio

A buffer solution simulating blood pH (7.4) needs a mole ratio of Na₂HPO₄ / NaH₂PO₄ of 1.6.

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Most basic sodium salt solution

A solution of NaD (the sodium salt of acid HD) will have the highest pH and be the most basic, given the pKa values provided.

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pH at Equivalence Point

At the equivalence point of a titration, the moles of acid and base are equal. For a weak acid/strong base titration, the pH at the equivalence point is greater than 7 because the conjugate base of the weak acid hydrolyzes water, producing OH- ions.

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Titration Calculation

To calculate the pH of a solution after a certain volume of titrant has been added, determine the moles of acid and base present, then use the appropriate equilibrium constant (Ka or Kb) to calculate the pH.

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Reduction

Reduction is the gain of electrons by a chemical species.

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Oxidation Number of Chromium

The oxidation number of an element in a compound represents its hypothetical charge if all bonds were ionic. In (NH4)2Cr2O7, the oxidation number of chromium is +6.

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Voltaic Cell Diagram

A voltaic cell diagram represents the components of a voltaic cell, including the anode, cathode, and the direction of electron flow. The anode is on the left, the cathode is on the right, and the double vertical line represents the salt bridge.

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Standard Reduction Potential

A measure of the tendency of a species to gain electrons and be reduced, expressed in volts (V). A more positive value indicates a stronger tendency for reduction.

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Oxidizing Agent

A species that gains electrons and is reduced in a redox reaction, causing another species to be oxidized.

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Reducing Agent

A species that loses electrons and is oxidized in a redox reaction, causing another species to be reduced.

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Stronger Reducing Agent

A species with a more negative standard reduction potential is a stronger reducing agent, as it is more easily oxidized.

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Electrochemical Cell

A device that converts chemical energy into electrical energy (galvanic cell) or vice versa (electrolytic cell) by utilizing redox reactions.

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Reaction Rate Conversion

Converting the rate of reaction from mols/h to mols/s involves dividing the given rate by 3600 (the number of seconds in an hour).

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Catalyst Effect

A catalyst provides an alternative reaction pathway with lower activation energy, resulting in a faster rate of reaction.

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First-Order Kinetics

In first-order kinetics, the reaction rate is directly proportional to the concentration of a single reactant.

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Second-Order Rate Constant

The rate constant (k) in a second-order reaction relates the rate to the square of the reactant concentration.

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Equilibrium Constant (K)

The equilibrium constant (K) indicates the relative amounts of products and reactants at equilibrium. A large K value indicates a higher concentration of products at equilibrium.

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Equilibrium: Rate of Reaction

At equilibrium, the forward and reverse reaction rates are equal, resulting in constant concentrations of reactants and products.

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Rate Constants at Equilibrium

Although the forward (kf) and reverse (kr) rate constants are not equal, the rates of the forward and reverse reactions become equal at equilibrium due to concentration changes.

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Oxidizing and Reducing Agents

An oxidizing agent gains electrons and is reduced, causing another species to be oxidized. A reducing agent loses electrons and is oxidized, causing another species to be reduced.

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Gibbs Free Energy

The Gibbs Free Energy (ΔG°) is a thermodynamic quantity that predicts the spontaneity of a reaction. It combines enthalpy change (ΔH°) and entropy change (ΔS°) at a constant temperature.

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Reaction Order

The overall order of a reaction determines how the reaction rate changes with reactant concentrations. It is the sum of the exponents in the rate law.

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Half-Life

The half-life (t1/2) of a reaction is the time it takes for the concentration of a reactant to decrease to half its initial value. It is a characteristic time scale for a first-order reaction.

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Acid-Base Reaction

In an acid-base reaction, an acid donates a proton (H+) to a base, forming a conjugate base and conjugate acid.

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Buffer Solution pH

A buffer solution resists changes in pH upon addition of small amounts of acid or base. It consists of a weak acid and its conjugate base, maintaining a relatively constant pH.

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Concentration Cell

A concentration cell uses the same half-reaction for both the anode and cathode, but with different concentrations. The potential difference arises from the concentration gradient.

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Rate Law Determination

The rate law expresses the relationship between the rate of a reaction and the concentrations of reactants. It is determined experimentally by analyzing the effect of changing reactant concentrations on the rate.

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Study Notes

Summary of Chemistry Concepts

  • Reduction: The gain of electrons in a chemical reaction.
  • Oxidation: The loss of electrons in a chemical reaction.
  • Voltaic Cell: A galvanic cell producing electricity from a spontaneous redox reaction.
  • Cell Diagram: A shorthand notation representing a voltaic cell.
  • Standard Reduction Potential (E°): The tendency of a species to be reduced in a half-reaction under standard conditions.
  • Nernst Equation: Used to calculate the cell potential under non-standard conditions.
  • Reaction Quotient (Q): A measure of the relative amounts of products and reactants present in a reaction at any given time.
  • Equilibrium Constant (K): A value that represents the ratio of products to reactants at equilibrium.
  • Equilibrium: The state where the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products no longer change significantly.
  • pH: A measure of the hydrogen ion concentration in a solution, signifying acidity or basicity. A measure for the acidity of the solution.
  • Reaction Order: The dependence of a reaction rate on the concentration of reactants.
  • Rate constant(k): A proportionality constant that relates the rate of a reaction to the concentrations of reactants
  • Half-life (t1/2): The time required for the concentration of a reactant to decrease to half its initial value in a chemical reaction.
  • Buffer Solution: A solution that resists changes in pH upon addition of small amounts of acid or alkali.
  • Solubility Product Constant (Ksp): Measure of solubility of a solid ionic compound.

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Description

This quiz covers essential chemistry concepts such as oxidation and reduction reactions, voltaic cells, standard reduction potentials, and equilibrium. It also delves into important equations like the Nernst Equation and the calculation of pH. Understanding these key topics is crucial for mastering chemistry.

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