Unit 2: Changes in Matter Review Answers 1) What form of energy is associated with the following illustrations? Radiant mechanical thermal Chemical/radiant/ thermal mechanical Radiant 2) Name at least two forms of energy that could be used to operate the following objects or systems a) A vehicle Chemical, mechanical, electrical b) A flashlight Chemical, radiant, electrical c) A calculator Chemical, radiant, electrical d) A power plant mechanical, electrical
3) Indicate whether the following are energy transformations or transfers and specify the type of energy involved. a) A wood fire Transformation: Chemical thermal b) A windmill Transfer: mechanical c) A cyclist eats a banana Transformation: Chemical mechanical 4) Name the phase change below, the initial state and final state of the substance and indicate whether energy is absorbed or released. a) Chocolate is melted to make candy Fusion/melting: solid, energy is absorbed b) Freezing food is an efficient conservation method. solidification: solid, energy is released c) Frost forms on cars in the winter deposition: solid, energy is released d) Dry ice disappears without a trace sublimation: solid, energy is absorbed 5) What are the signs that a chemical change has occurred? Colour change, heat/light absorbed or released, precipitate or formation 6) During a dissolution, how do you know if the resulting solution absorbed or released energy? Released temperature of solution (surroundings) goes up Absorbed temperature of solution (surroundings) goes down
7) The graph was drawn from data collected as a substance was heated at a constant rate. Use the graph to answer the following questions. a) Fill in the blanks: At point A, the beginning of observations, the substance exists in a solid state. Material in this fixed phase has volume and shape. With each passing Thermal energy minute, is added to the substance. This causes the molecules of the substance to more rapidly which we detect by a rise in the substance. At point B, the temperature of the substance is C. The solid melt begins to. At point C, the substance is completely or in a state. Material in this phase has volume and variable move fixed shape. The energy put to the substance between minutes 5 and 9 was used to convert the substance from a to a. This heat energy is called the heat of fusion. (An interesting fact.) Between 9 and 13 minutes, the added energy increases the of the substance. During the time from point D to point E, the is. By point E, the substance is variable fixed completely in the phase. Material in this phase has volume and shape. The energy put to the substance between minutes 13 and 18 converted the substance from a to a state. This heat energy is called the heat of vaporization. (An interesting fact.) Beyond point E, the substance is still in the phase, but the molecules are moving faster solid temperature changing state as indicated by the increasing temperature. temperature 70 o C melted variable
b) Which of these three substances was likely used in this phase change experiment? Explain your answer Foosium because the melting point on the graph is 70 o C and the boiling point is 140 o C. Both are characteristic properties that can be used to identify a substance Substance Melting point Boiling point Bolognium 20 C 100 C Unobtainium 40 C 140 C Foosium 70 C 140 C 8) Name the changes in the phases below and indicated the function of energy in these phase changes. Solid solid Energy is being absorbed causing the particles to move faster and thus further apart Energy is being released causing the particles to move slower and closer together 9) Robert adds 25 ml of water to a 50 ml solution causing the concentration to become 20 g/l. What was the concentration of the solution before dilution? C 1 =? V 1 = 50 ml (0.05L) C 2 = 20 g/l V 2 = 25 ml + 50 ml = 75 ml (0.075 L) C 1 V 1 = C 2 V 2 C 1 (0.05) = (20)(0.075) C 1 = 30 g/l
10) Through the process of dilution, you have made 400 ml of a 20 g/l solution. Since the original concentration was 80 g/l, what volume of the original solution did you use? C 1 = 80 g/l V 1 =? C 2 = 20 g/l V 2 = 400 ml (0.400 L) C 1 V 1 = C 2 V 2 80V 1 = (20)(0.400) C 1 = 0.1 L or 100 ml 11) Roger pours 75 ml of a 50 g/l solution into a beaker and dilutes it by adding 25 ml of water. Calculate the new concentration of Roger s solution. C 1 = 50 g/l V 1 = 75 ml (0.075L) C 2 =? V 2 = 25 ml + 75 ml = 100 ml (0.1 L) C 1 V 1 = C 2 V 2 (50)(0.075) = C 2 (0.1) 37.5 g/l = C 2
Flashback 12) The table below shows information about four solutions. Solution Quantity of salt in the solution Volume of the solution 1 2.0 g 500 ml = 0.5 L 2 1.0 g 1.5 L 3 3.0 g 2.0 L 4 6.0 g 3.0 L Which solution has the LOWEST concentration? Show Work Use C= in this case change volume to L and compare concentration in g/l Solution 1 C= = = 4g/L Solution 2 C= = = 0.67g/L Solution 3 C= = = 1.5 g/l Solution 4 C= = = 2 g/l Solution 2 has the lowest concentration