Unit 6 MCQ Study Guide

The following questions relate to the below information. XY2 → X + Y2 The equation above represents the decomposition of a compound XY2. The diagram below shows two reaction profiles (path one and path two) for the decomposition of XY2. Which of the following best describes the flow of heat when 1.0 mol of XY2 decomposes? Responses A 50 kJ of heat is transferred to the surroundings. B 50 kJ of heat is transferred from the surroundings. C 100 kJ of heat is transferred to the surroundings. D 100 kJ of heat is transferred from the surroundings.

B 50 kJ of heat is transferred from the surroundings.

A 100g sample of a metal was heated to 100oC and then quickly transferred to an insulated container holding 100g of water at 22oC. The temperature of the water rose to reach a final temperature of 35oC. Which of the following can be concluded? Responses A The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained. B The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained. C The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water. D The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.

B The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

A 30.g sample of Al(s) is heated to 50°C and placed in a calorimeter containing 150g of water at 20°C. As the system approaches thermal equilibrium, energy is transferred Responses A from the Al(s) to the water and the temperature of the water decreases B from the Al(s) to the water and the temperature of the Al(s) decreases C from the water to the Al(s) and the temperature of the water increases D from the water to the Al(s) and the temperature of the Al(s) increases

B from the Al(s) to the water and the temperature of the Al(s) decreases

K(s)+ ½ Cl2(g) → KCl(s) ΔH° = -437kJ/molrxn The elements K and Cl react directly to form the compound KCl according to the equation above. Refer to the information above and the table below to answer the questions that follow. Which of the values of ∆Ho for a process in the table is (are) less than zero (i.e., indicate(s) an exothermic process)? Responses A z only B y and z only C x, y, and z only D w, x, y, and z

B y and z only

When a 50.mL sample of C2H5OH is mixed with a 50.mL sample of H2O, the resulting mixture has a volume of 95mL, and the container is warm to the touch. Which of the following best describes these observations? Responses A A chemical reaction occurs, as evidenced by the volume of the resultant mixture being less than the total volume of the initial components. B A chemical change occurs, as evidenced by the formation of new covalent bonds releasing more energy than is absorbed by the breaking of the existing covalent bonds. C A physical change occurs, and the solvation process is exothermic. D A physical change occurs, and the solvation process is endothermic.

C A physical change occurs, and the solvation process is exothermic.

A 50mL sample of C6H14(l) is mixed with a 50mL sample of H2O(l), and the mixture is shaken vigorously. The two liquids do not stay mixed but instead form two separate layers. The density of hexane is 0.66g/mL, and the density of water is 1.00g/mL. A 1.0g sample of I2(s) is added to the mixture, which is shaken again. Which of the following best predicts what happens to the I2(s) ? Responses A I2 will be found mainly in the top layer because it will dissolve more in the H2O(l). B I2 will be found mainly in the bottom layer because it will dissolve more in the H2O(l). C I2 will be found mainly in the top layer because it will dissolve more in the C6H14(l). D I2 will be found mainly in the bottom layer because it will dissolve more in the C6H14(l).

C I2 will be found mainly in the top layer because it will dissolve more in the C6H14(l).

A piece of Fe(s) at 25°C is placed into H2O(s) at 75°C in an insulated container. A student predicts that when thermal equilibrium is reached, the Fe atoms, being more massive than the H2O molecules, will have a higher avg kinetic e than the H2O molecules. Why is the student's prediction incorrect? Responses A At TE, the less massive H2O molecules would have a higher avg kinetic e than the Fe atoms bc theyre more free to move than the Fe atoms. B At TE, the collisions between the Fe atoms and the H2O molecules would cease because the avg kinetic e of their particles would be the same. C At TE, the movement of both the Fe atoms and the H2O molecules would cease; thus, the avg kinetic e of their particles would have to be the same. D At TE, the avg kinetic e of the Fe atoms can't be greater than the H2O molecules; the avg kinetic e's must be the same according to the definition of thermal equilibrium.

D At thermal equilibrium, the average kinetic energy of the Fe atoms cannot be greater than that of the H2O molecules; the average kinetic energies must be the same according to the definition of thermal equilibrium.

Which of the following best helps to explain why hexane has a higher boiling point than methanol has? Responses A Methanol molecules can form hydrogen bonds with other methanol molecules. B Hexane cannot form hydrogen bonds with other hexane molecules. C Methanol molecules have attractions to one another due to London dispersion forces. D Hexane molecules have electron clouds that are larger than those of methanol molecules.

D Hexane molecules have electron clouds that are larger than those of methanol molecules.

A student was given samples of four different unknown liquids. The unknown liquids are propylamine, pentane, 2-propanol, and propanoic acid. The structures and molar masses of the compounds are shown in the table above. On the basis of this information, the student designed some experiments to identify the samples. Which of the following statements correctly identifies which compound, pentane or propanoic acid, has the higher boiling point and provides a valid justification? Responses A Pentane, because it has greater London dispersion forces than propanoic acid does B Pentane, because it can form more hydrogen bonds per molecule than propanoic acid can C Propanoic acid, because double bonds are harder to break than single bonds D Propanoic acid, because it forms hydrogen bonds, whereas pentane does not

D Propanoic acid, because it forms hydrogen bonds, whereas pentane does not

The dissolution of an ionic solute in a polar solvent can be imagined as occurring in three steps, as shown in the figure above. In step 1, the separation between ions in the solute is greatly increased, just as will occur when the solute dissolves in the polar solvent. In step 2, the polar solvent is expanded to make spaces that the ions will occupy. In the last step, the ions are inserted into the spaces in the polar solvent. Which of the following best describes the enthalpy change, ΔH, for each step? Responses A All three steps are exothermic. B All three steps are endothermic. C Steps 1 and 2 are exothermic, and the final step is endothermic. D Steps 1 and 2 are endothermic, and the final step is exothermic.

D Steps 1 and 2 are endothermic, and the final step is exothermic.