Problem 54 - Chemistry The Central Science

Question

Consider the following equation: $$\mathrm{Ca}^{+}(g)+\mathrm{e}^{-} \longrightarrow \mathrm{Ca}(g)$$ Which of the following statements are true? (i) The energy change for this process is the electron affinity of the Ca' ion. (ii) The energy change for this process is the negative of the first ionization energy of the Ca atom. (ii) The energy change for this process is the negative of the electron affinity of the Ca atom.

Step-by-Step Solution

Answer

The correct statement is (ii): The energy change for this process is the negative of the first ionization energy of the Ca atom. Statement (i) is incorrect because electron affinity refers to neutral atoms, not charged ions like Ca+. Statement (iii) is also incorrect because the energy change is not related to the electron affinity of the Ca atom, since an electron is being added to a Ca+ ion, not a neutral Ca atom.

Step 1: 1. Analyze Statement (i)

: Statement (i) says that the energy change for this process is the electron affinity of the Ca+ ion. Electron affinity refers to the change in energy when an electron is added to a neutral atom to form a negatively charged ion. In this case, an electron is being added to a Ca+ ion. Therefore, we need to analyze whether the energy change corresponds to the electron affinity.

Step 2: 2. Analyze Statement (ii)

: Statement (ii) states that the energy change for this process is the negative of the first ionization energy of the Ca atom. Ionization energy refers to the energy required to remove an electron from an atom or ion. The first ionization energy specifically refers to the energy required to remove the first electron from the neutral atom. In this case, since an electron is being added to the positive Ca+ ion, we should analyze whether the energy change is equal to the negative of the first ionization energy of the Ca atom.

Step 3: 3. Analyze Statement (iii)

: Statement (iii) says that the energy change for this process is the negative of the electron affinity of the Ca atom. As we have mentioned before, electron affinity refers to the change in energy when an electron is added to a neutral atom to form a negatively charged ion. Here, an electron is being added to a Ca+ ion; therefore, we need to analyze if the energy change is equal to the negative of the electron affinity of the Ca atom.

Step 4: 4. Identify the correct statement(s)

: Statement (i) is incorrect because the energy change is not related to the electron affinity of the Ca+ ion, since electron affinity refers specifically to the addition of an electron to a neutral atom, not to a charged ion like Ca+. Statement (ii) is correct because the energy change can be considered the negative of the first ionization energy of the Ca atom. This is because ionization energy is the energy required to remove an electron (form a positive ion), while in our case an electron is being added (forming a neutral atom). Therefore, the energy change is the opposite of the ionization energy. Statement (iii) is incorrect because the energy change is not related to the electron affinity of the Ca atom. While the process involves the addition of an electron, it is not being added to a neutral Ca atom, but rather to a Ca+ ion.

Key Concepts

Electron Affinity

Electron affinity is all about the energy change when we add an electron to a neutral atom. It measures how much energy is released when an electron is added. Think of it as a tug of war between the electron and the atom. If the atom "wants" the electron, energy is released, showing a negative value. For electron affinity to be applicable, the starting point should be a neutral atom, not an already charged ion.

When an electron joins a neutral atom, that energy change gives your electron affinity. In summary:

• Enhances understanding of an atom's ability to gain electrons
• Affects chemical behaviors like bond formation
• More negative values mean stronger attraction to electrons

The original exercise involved adding an electron to a positively charged calcium ion (Ca⁺). Hence, electron affinity doesn't apply there as it starts with an already charged ion.

Chemical Reactions

Chemical reactions engage in the transformation of substances. During these processes, bonds are made or broken, transforming reactants into products. Energy plays a critical role in chemical reactions since it’s either absorbed or released.

In the exercise, a chemical reaction occurs when an electron is added to a calcium ion (Ca⁺), forming a neutral calcium atom (Ca). This demonstrates:

• How energy can be linked to breaking or forming chemical bonds
• The transfer of electrons, known as redox reactions
• Influence of chemical reactions on the energy state of substances

Understanding these processes helps in predicting how substances will interact and change during chemical reactions.

Calcium Ion

Calcium, with the chemical symbol Ca, is a versatile element commonly found in stones and bones. When it loses two electrons, it becomes the calcium ion, denoted as Ca²⁺. In our exercise, the ion involved was a singly charged calcium ion, Ca⁺.

Why is calcium so important?

• Calcium ions play vital roles in biological processes such as muscle contractions and nerve signaling.
• In chemistry, they react and bind with various substances, forming compounds like calcium carbonate (CaCO₃) found in limestone.
• Calcium ions tend to have low electron affinity since forming a stable electron configuration makes them reactive in specific environments.

In the context of the exercise, it’s important to appreciate the nuances of how calcium ion transitions can affect energy states.