Passage
The alkaline-earth metals are a highly reactive family of metals occupying Group 2 (IIA) of the periodic table. In their elemental form, the alkaline-earth metals have a shiny, silvery-white to slightly yellowish appearance. The alkaline-earth metals exhibit some similarities to the chemistry of the alkali metals (Group 1) but are a little less reactive.Atoms of the alkaline-earth metals (M) have only two valence electrons and a low first and second ionization energy. Consequently, these metals readily lose both electrons to produce cations with a +2 charge (M⁺²) during reactions with nonmetals. As a result, the alkaline-earth metals do not exist in their elemental metallic form in nature. Instead, the Group 2 elements are found primarily as metal oxides, which form by reacting oxygen (Reaction 1) .

Similarly, elemental samples of alkaline-earth metals will react with elemental halogens (X₂) to form metal halides (Reaction 2) , all of which are ionic except for BeCl₂.

Except for beryllium, the alkaline-earth metals react with water to produce very basic metal hydroxide solutions and hydrogen gas (Reaction 3) .

The most difficult alkaline-earth metal to study is radium, because it is a rare radioactive element that is produced from the nuclear decay of uranium. The most common natural isotope, radium-226, has a half-life of 1,600 years and decays by alpha emission into radon-222 (Reaction 4) .

-Which of the following diagrams correctly labels the activation energy E_a for the reaction shown in Figure 1?

Question

Passage
The alkaline-earth metals are a highly reactive family of metals occupying Group 2 (IIA) of the periodic table. In their elemental form, the alkaline-earth metals have a shiny, silvery-white to slightly yellowish appearance. The alkaline-earth metals exhibit some similarities to the chemistry of the alkali metals (Group 1) but are a little less reactive.Atoms of the alkaline-earth metals (M) have only two valence electrons and a low first and second ionization energy. Consequently, these metals readily lose both electrons to produce cations with a +2 charge (M⁺²) during reactions with nonmetals. As a result, the alkaline-earth metals do not exist in their elemental metallic form in nature. Instead, the Group 2 elements are found primarily as metal oxides, which form by reacting oxygen (Reaction 1) .

Similarly, elemental samples of alkaline-earth metals will react with elemental halogens (X₂) to form metal halides (Reaction 2) , all of which are ionic except for BeCl₂.

Except for beryllium, the alkaline-earth metals react with water to produce very basic metal hydroxide solutions and hydrogen gas (Reaction 3) .

The most difficult alkaline-earth metal to study is radium, because it is a rare radioactive element that is produced from the nuclear decay of uranium. The most common natural isotope, radium-226, has a half-life of 1,600 years and decays by alpha emission into radon-222 (Reaction 4) .

-Which of the following diagrams correctly labels the activation energy E_a for the reaction shown in Figure 1?

Quizplus · Accepted Answer

11ecba2d_11e6_8f32_a3bf_4b949e979090_MD0008_00 As existing bonds are broken and new bonds are formed for the conversion of a reactant to a product, the elevated energy necessary to form a transition state acts as an energy barrier that must be overcome for the reaction to proceed. The transition state (‡) with the highest energy (relative to the reactants) presents an energy barrier to the overall reaction. Therefore, the energy necessary to achieve the highest energy transition state is the minimum energy needed to activate the reactants sufficiently for the completion of the reaction (the activation energy). In a reaction free-energy diagram, transition states are seen graphically as energy maxima (peaks). The highest energy transition state (tallest peak relative to the reactant energy) is the greatest energy barrier for the overall reaction and determines the activation energy E_a. Therefore, E_a is the energy difference between the highest peak and the reactants (peak energy minus reactant energy). (Choice B) This is the energy difference between the intermediate and the reactants. The activation energy is larger because the highest energy transition state must be reached to form the intermediate of this reaction. (Choice C) This is the overall change in energy for the reaction to form Compound 3. This does not reflect the energy required to achieve the highest energy transition state along the reaction pathway. (Choice D) This is the energy difference between the intermediate and Compound 2. This shows the relative change in energy between the species, but it does not reflect the activation energy associated with the highest energy transition state. Educational objective: The activation energy is the minimum energy needed to reach the highest energy transition state that enables the completion of a reaction. In a reaction free-energy diagram, the activation energy is the energy difference between the tallest peak (relative to the reactants) and the reactants (peak energy minus reactant energy).