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<div style="margin-top: 1px; margin-bottom: 20px; border: 1px solid #ddd; border-radius: 5px; overflow: hidden; box-sizing: border-box;"><div style="background: #f5f5f5; padding: 10px 15px; border-bottom: 1px solid #ddd;"><h4 style="margin: 0; font-size: 13pt; text-decoration: underline;"><span style="color: #0000ff; font-weight: bold;">Questions 7–9</span></h4></div><div style="padding: 15px; background: #fff; line-height: 1.65; font-family: Georgia, Palatino, serif; font-size: 12pt;"><p style="margin-top: 0;"><strong>Questions 7–9 refer to the following information.<img class="aligncenter wp-image-433370" src="https://www.iitianacademy.com/wp-content/uploads/2025/11/Screenshot-2025-11-01-193518.png" alt="" width="750" height="180" /></strong></p><p>At \(27^{\circ}\text{C}\), five identical rigid \(2.0\) L vessels are filled with \(N_{2}(g)\) and sealed. Four of the five vessels also contain a \(0.050\) mol sample of \(NaHCO_{3}(s)\), \(NaBr(s)\), \(Cu(s)\), or \(I_{2}(s)\) as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of \(N_{2}(g)\) in each vessel is \(720\) mm Hg. All four vessels are heated to \(127^{\circ}\text{C}\) and allowed to reach a constant pressure.</p><div style="margin: 10px 0; text-align: center;"> </div></div></div><div style="margin-top: 18px; border: 1px solid #ddd; border-radius: 5px; overflow: hidden;"><div style="background: #f5f5f5; padding: 10px 15px; border-bottom: 1px solid #ddd;"><h4 style="margin: 0; font-size: 13pt; text-decoration: underline;"><span style="color: #0000ff; font-weight: bold;">Question 7</span></h4></div><div style="padding: 15px; background: #fff; font-family: Georgia,Palatino,serif; font-size: 12pt; line-height: 1.65;"><p>At \(127^{\circ}\text{C}\), the pressure in vessel 1 is found to be higher than that in vessel 2. Which of the following reactions best accounts for the observation?</p><div style="margin: 10px 0; padding-left: 20px;">(A) \(NaHCO_{3}(s)\rightarrow Na(s)+HCO_{3}(s)\)<br />(B) \(NaHCO_{3}(s)\rightarrow NaH(s)+CO_{3}(s)\)<br />(C) \(2~NaHCO_{3}(s)\rightarrow Na_{2}CO_{3}(s)+CO_{2}(g)+H_{2}O(g)\)<br />(D) \(2~NaHCO_{3}(s)+N_{2}(g)\rightarrow2~NaNO_{3}(s)+C_{2}H_{2}(g)\)</div></div></div><div style="margin-top: 10px; border: 1px solid #ddd; border-radius: 5px; background: #fff; padding: 10px;"><details><summary style="color: #ff00ff; cursor: pointer; font-weight: bold; font-family: Georgia,Palatino,serif; font-size: 13pt;">▶️ Answer/Explanation</summary><div style="margin-top: 12px; padding: 10px; background: #f9f9f9; border-left: 3px solid #ccc; line-height: 1.65; font-family: Georgia, Palatino, serif; font-size: 12pt;"><p><b>1. Analyze the Observation:</b><br />Both vessels start with the same pressure of \(N_2(g)\). After heating, vessel 1 (\(NaHCO_3\)) has a higher pressure than vessel 2 (\(NaBr\)).</p><p><b>2. Inference:</b><br />By the Ideal Gas Law, pressure is proportional to moles (\(n\)) at constant V and T. The higher pressure must be due to an <b>increase in the total moles of gas</b>. This means \(NaHCO_3(s)\) decomposed to produce gas, while \(NaBr(s)\) did not.</p><p><b>3. Evaluate Options:</b><br />Only reaction (C) shows \(NaHCO_3(s)\) decomposing to produce gaseous products (\(CO_2(g)\) and \(H_2O(g)\)), which would increase the pressure. <br />✅ <strong>Answer: (C)</strong></p></div></details></div><div style="margin-top: 18px; border: 1px solid #ddd; border-radius: 5px; overflow: hidden;"><div style="background: #f5f5f5; padding: 10px 15px; border-bottom: 1px solid #ddd;"><h4 style="margin: 0; font-size: 13pt; text-decoration: underline;"><span style="color: #0000ff; font-weight: bold;">Question 8</span></h4></div><div style="padding: 15px; background: #fff; font-family: Georgia,Palatino,serif; font-size: 12pt; line-height: 1.65;"><p>At \(127^{\circ}\text{C}\), the entire sample of \(I_{2}\) is observed to have vaporized. How does the mass of vessel 5 at \(127^{\circ}\text{C}\) compare to its mass at \(27^{\circ}\text{C}\)? </p><div style="margin: 10px 0; padding-left: 20px;">(A) The mass is less, since the \(I_{2}\) is in the vapor phase.<br />(B) The mass is the same, since the number of each type of atom in the vessel is constant.<br />(C) The mass is greater, since the \(I_{2}\) will react with \(N_{2}\) to form \(NI_{3}\), which has a greater molar mass.<br />(D) The mass is greater, since the pressure is greater and the particles have a higher average kinetic energy.</div></div></div><div style="margin-top: 10px; border: 1px solid #ddd; border-radius: 5px; background: #fff; padding: 10px;"><details><summary style="color: #ff00ff; cursor: pointer; font-weight: bold; font-family: Georgia,Palatino,serif; font-size: 13pt;">▶️ Answer/Explanation</summary><div style="margin-top: 12px; padding: 10px; background: #f9f9f9; border-left: 3px solid #ccc; line-height: 1.65; font-family: Georgia, Palatino, serif; font-size: 12pt;"><p><b>1. Apply Law of Conservation of Mass:</b><br />The vessel is a <b>sealed system</b>. No matter can enter or leave.</p><p><b>2. Analyze the Process:</b><br />The change \(I_2(s) \rightarrow I_2(g)\) is a physical phase change (sublimation). The number of \(I\) atoms and \(N\) atoms inside the sealed vessel remains constant.</p><p><b>3. Conclusion:</b><br />Because the number of atoms of each element is constant, the total mass must also be constant, regardless of the temperature, pressure, or phase. <br />✅ <strong>Answer: (B)</strong></p></div></details></div><div style="margin-top: 18px; border: 1px solid #ddd; border-radius: 5px; overflow: hidden;"><div style="background: #f5f5f5; padding: 10px 15px; border-bottom: 1px solid #ddd;"><h4 style="margin: 0; font-size: 13pt; text-decoration: underline;"><span style="color: #0000ff; font-weight: bold;">Question 9</span></h4></div><div style="padding: 15px; background: #fff; font-family: Georgia,Palatino,serif; font-size: 12pt; line-height: 1.65;"><p><img class="size-full wp-image-433375 aligncenter" src="https://www.iitianacademy.com/wp-content/uploads/2025/11/Screenshot-2025-11-01-193933.png" alt="" width="233" height="172" /></p><p>The gas particles in vessel 3 at \(27^{\circ}\text{C}\) are represented in the diagram above. The lengths of the arrows represent the speeds of the particles. Which of the following diagrams best represents the particles when vessel 3 is heated to \(127^{\circ}\text{C}\)? [cite: 105-107]</p><div style="margin: 10px 0; padding-left: 20px;">(A) <img class="alignnone size-full wp-image-433379" src="https://www.iitianacademy.com/wp-content/uploads/2025/11/Screenshot-2025-11-01-194053.png" alt="" width="182" height="144" /><br />(B) <img class="alignnone size-full wp-image-433380" src="https://www.iitianacademy.com/wp-content/uploads/2025/11/Screenshot-2025-11-01-194102.png" alt="" width="195" height="154" /><br />(C) <img class="alignnone size-full wp-image-433381" src="https://www.iitianacademy.com/wp-content/uploads/2025/11/Screenshot-2025-11-01-194111.png" alt="" width="198" height="155" /><br />(D) <img class="alignnone size-full wp-image-433382" src="https://www.iitianacademy.com/wp-content/uploads/2025/11/Screenshot-2025-11-01-194118.png" alt="" width="177" height="155" /></div></div></div><div style="margin-top: 10px; border: 1px solid #ddd; border-radius: 5px; background: #fff; padding: 10px;"><details><summary style="color: #ff00ff; cursor: pointer; font-weight: bold; font-family: Georgia,Palatino,serif; font-size: 13pt;">▶️ Answer/Explanation</summary><div style="margin-top: 12px; padding: 10px; background: #f9f9f9; border-left: 3px solid #ccc; line-height: 1.65; font-family: Georgia, Palatino, serif; font-size: 12pt;"><p><b>1. Analyze the Process:</b><br />Heating the gas from \(27^{\circ}\text{C}\) to \(127^{\circ}\text{C}\) increases the average kinetic energy of the particles. Since \(KE = \frac{1}{2}mv^2\), this means the average speed (\(v\)) increases.</p><p><b>2. Analyze the Diagram:</b><br />The original diagram shows 4 diatomic \(N_2\) molecules. The arrows should become <b>longer</b> to represent higher speed. The number of molecules (\(4\)) and their diatomic nature (\(N_2\)) should not change in this sealed vessel.</p><p><b>3. Conclusion:</b><br />Diagram (A) correctly shows the same 4 diatomic molecules, but with longer arrows indicating a higher speed. <br />✅ <strong>Answer: (A)</strong></p></div></details></div>