This chemistry question involves key chemical concepts and calculations. The detailed solution below walks through each step, from identifying the reaction type to computing the final answer.
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Here's the solution to Question 3: 3.1 The reaction is referred to as heterogeneous because the reactants and products are not all in the same physical state. Carbon (C) is a solid, while oxygen (O_2) and carbon dioxide (CO_2) are gases. 3.2 Step 1: Calculate the initial moles of carbon. Molar mass of C = 12.01 g/mol. Initial moles of C = massmolar mass = 3.8 g12.01 g/mol ≈ 0.3164 mol Step 2: Determine the moles of carbon that reacted. At equilibrium, 0.292 mol of carbon remained. Moles of C reacted = Initial moles of C - Equilibrium moles of C Moles of C reacted = 0.3164 mol - 0.292 mol = 0.0244 mol Step 3: Set up an ICE (Initial, Change, Equilibrium) table for moles. The reaction is: C(s) + O_2(g) CO_2(g) Let the initial moles of O_2 be X. The volume of the flask is 1000 cm^3 = 1 dm^3, so moles are equal to concentrations. | Species | Initial (mol) | Change (mol) | Equilibrium (mol) | | :------------------ | :------------ | :----------- | :---------------- | | C(s) | 0.3164 | -0.0244 | 0.292 | | O_2(g) | X | -0.0244 | X - 0.0244 | | CO_2(g) | 0 | +0.0244 | 0.0244 | Step 4: Write the equilibrium constant expression and substitute values. For heterogeneous reactions, solids are excluded from the K_c expression. K_c = [CO_2][O_2] Given K_c = 0.145. 0.145 = (0.0244)/(X - 0.0244) Step 5: Solve for X (initial moles of O_2). 0.145(X - 0.0244) = 0.0244 0.145X - (0.145 × 0.0244) = 0.0244 0.145X - 0.003538 = 0.0244 0.145X = 0.0244 + 0.003538 0.145X = 0.027938 X = (0.027938)/(0.145) ≈ 0.192676 mol Step 6: Calculate the initial mass of oxygen (O_2). Molar mass of O_2 = 2 × 16.00 = 32.00 g/mol. Mass of O_2 = moles × molar mass Mass of O_2 = 0.192676 mol × 32.00 g/mol ≈ 6.1656 g Rounded to two decimal places: The initial mass of oxygen (O_2) placed in the flask is 6.17 g. 3.3.1 Le Chatelier's principle states that if a change of condition (such as temperature, pressure, or concentration) is applied to a system in equilibrium, the system will shift in a direction that relieves the stress and re-establishes a new equilibrium. 3.3.2 The equilibrium constant (K_c) only changes with temperature. Since the K_c value increased, the condition that was changed is temperature. 3.3.3 The forward reaction is ENDOTHERMIC. Explanation: An increase in the K_c value indicates that the equilibrium shifted to the right, favoring the formation of products. According to Le Chatelier's principle, if the temperature of a system at equilibrium is increased, the system will shift in the direction that absorbs heat (the endothermic direction) to counteract the increase in temperature. Since the equilibrium shifted to the right (product side), the forward reaction must be endothermic. That's 4 down. 1 left today — send the next one.