Radioactivity and Half-Life Calculations
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Questions and Answers

How much cesium-137 would be remaining after 90 years if 1.0 g initially disintegrates over that period?

  • 0.25 g
  • 0.125 g (correct)
  • 0.5 g
  • 0.75 g

What is the final amount of actinium-226 remaining after 58 hours if starting with 100 mg?

  • 50 mg
  • 70 mg
  • 25 mg (correct)
  • 10 mg

Which element is produced during the beta decay of 234Pa?

  • Plutonium-238
  • Uranium-234 (correct)
  • Radium-226
  • Cobalt-60

What is the total change in enthalpy (ΔH) during the dissolution of CaCl2(s)?

<p>-795.8 kJ (B)</p> Signup and view all the answers

How much heat is released when 3.40 mol of Fe2O3 reacts with CO?

<p>89.42 kJ (A)</p> Signup and view all the answers

In the reaction 2Na2SO3 + O2 → 2Na2SO4, which element is oxidized?

<p>O<sub>2</sub> (B)</p> Signup and view all the answers

Which species acts as the reducing agent in the reaction 2FeCl3 + H2S → 3FeCl2 + 2HCl + S?

<p>H<sub>2</sub>S (B)</p> Signup and view all the answers

In the balanced equation 2MnO4- + 16H+ + 10I- → 2Mn2+ + 8H2O + 5I2, what is the oxidation state of manganese in MnO4-?

<p>+7 (A)</p> Signup and view all the answers

Which of the following reactions shows alpha decay?

<p><sup>230</sup><sub>90</sub>Th → <sup>226</sup><sub>88</sub>Ra + <sup>4</sup><sub>2</sub>He (B)</p> Signup and view all the answers

When balancing the half-reaction for the reduction of Cu2+ to Cu, how many electrons are needed?

<p>2 (A)</p> Signup and view all the answers

In the context of redox reactions, what is the function of an oxidizing agent?

<p>To gain electrons (A)</p> Signup and view all the answers

In the reaction 3Mg + N2 → Mg3N2, which element is reduced?

<p>N<sub>2</sub> (D)</p> Signup and view all the answers

How many water molecules are produced in the balanced equation for the reaction of Cu2+ with SO32-?

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

Flashcards

Half-life

The time it takes for half of a radioactive substance to decay. This is a constant for each radioactive isotope.

Binding Energy

A measure of the energy released when the nucleus of an atom is formed. This is the energy required to break apart the nucleus.

Gibbs Free Energy (ΔG)

The change in Gibbs free energy that occurs during a chemical reaction. It is a measure of the spontaneity of a reaction.

Enthalpy Change (ΔH)

The enthalpy change that occurs during a chemical reaction. It is a measure of the heat absorbed or released during the reaction.

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Entropy Change (ΔS)

The entropy change that occurs during a chemical reaction. It measures the change in randomness or disorder of a system.

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Oxidizing Agent

The reactant that gains electrons and is reduced during a redox reaction.

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Reducing agent

The reactant that loses electrons and is oxidized during a redox reaction.

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Oxidation

The half-reaction where electrons are lost, resulting in an increase in oxidation number.

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Reduction

The half-reaction where electrons are gained, resulting in a decrease in oxidation number.

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Redox Reaction

A chemical reaction involving the transfer of electrons between reactants, resulting in a change in oxidation states.

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Alpha Decay

A process that involves the emission of an alpha particle (42He) from a radioactive nucleus.

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Beta Decay

A process that involves the emission of a beta particle (0-1β) from a radioactive nucleus.

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Balancing Redox Reactions

Balancing a redox reaction by adjusting coefficients to ensure the number of atoms and electrons on both sides of the equation are equal.

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Study Notes

Radioactivity and Half-Life Calculations

  • Half-life of Isotope X: 2.0 years
    • 4.0 mg sample decays to 0.50 mg in 6 years
  • Half-life of Selenium-93: 25.0 minutes
    • 10.0 mg decays to 0.50 mg in 108 minutes

Plutonium-238 Decay

  • Half-life: 87.74 years
    • Sample is 438.7 years old if only 3.125% remains radioactive

Plutonium-239 Decay

  • Half-life: 24,000 years.
    • It takes 79,729 years for a sample of Pu to decay to 10% of its original mass.

Nuclear Reactions (Completing Equations)

  • Alpha decay of U: U → Th + He
  • Alpha decay of 230Th: 230Th → 226Ra + He
  • Beta decay of Th: 234Th → 234Pa + e⁻
  • Beta decay of Pa: 234Pa → 234U + e⁻
  • Np-237 alpha decay: 237Np → 233Pa + He

Half-life of Cesium-137

  • Half-life: 30 years
    • 1.0 g of cesium-137 decays over 90 years, remaining 0.125 g.

Half-life of Actinium-226

  • Half-life: 29 hours
    • 100 mg of actinium-226 decays in 58 hours, remaining 25 mg

Balancing Redox Reactions (Acidic, Basic Conditions)

  • Identifying oxidizing and reducing agents: In redox reactions, identify the element reduced and the element oxidized. Oxidizing agents cause oxidation, while reducing agents cause reduction. Acidic or basic conditions influence these reactions, so make appropriate adjustments.

Enthalpy, Entropy, and Gibbs Free Energy Calculation

  • Calculating temperature for a reaction using the formula ΔG = ΔH - TΔS (Gibbs Free Energy)
    • Calculations are given by the provided examples.

Thermochemistry of CaCl₂ Dissolving (ΔH, ΔS)

  • Calculating temperature using ΔG = ΔH - TΔS. Calculation provided.

Exothermic Reaction (Iron and Carbon Dioxide Production)

  • Given formula and stoichiometric amounts for calculating amount of heat produced. - Calculate heat produced when a certain amount of Fe₂O₃ reacts with carbon monoxide, given an exothermic reaction. Calculate the kilojoules.

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Description

This quiz covers various aspects of radioactivity, focusing on half-life calculations and nuclear decay processes. You will explore the half-lives of different isotopes, including Plutonium-238 and Cesium-137, as well as completing nuclear reaction equations. Test your knowledge on the principles of radioactivity and decay!

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