Question

MULTIPLE CHOICE |18 pt-3 pt each): In this section, you are expected to select the best answer out of the optionsgiven. No partial credit will be given. Only one answer may be chosen ifthe answer is not obvious it will be considered incomplete. When heating a solution, a scientist detects a temperature increase in the solution overtime. Which of the following statements accurately characterizes the solution during this period? 1. The solution is at its boiling point The velocity of the molecules in the solution is increasing The solution is undergoing a phase change The solution is at its melting point a. b. c. d. 2. If you add a lot of ice to a cup of hot tea and after waiting 30 minutes there is still ice in the tea cup, what can you conclude about the temperature of the liquid in the cup? 23 C-room temperature a, b. 0 C-freezing point 10 C-just above freezing c. d. 40 C-much above freezing 3. Suppose that object A and object B have the same temperature and different masses. temperature of Č is unknown. To claim that all objects are in thermal equilibrium, They must contain the same amount of heat a. b. They must contain the same amount of work They must all be the same temperature c. d. All the above must be true 4. What does heat capacity depend on? The mass and material a. b. The mass and the temperature The mass and the heat c. d. The temperature and the material Engines use hot and cold reservoirs to produce work. Which of the following is true about engines? 5. a. They use heat from a cold reservoir to produce work and dump excess heat into a b. They use heat from a hot reservoir to produce work and dump excess heat intoa c. They use heat from a hot reservoir to consume work and dump excess heat into a d. They use heat from a cold reservoir to consume work and dump excess heat into a hot reservoir. cold reservoir. cold reservoir. hot reservoir 6. If you take a tray of baked cookies out of the oven, the tray cools off much fastr because.. a. b. c. d. The tray has a higher specific heat. The cookies have a higher specific heat. The tray has a lower specific heat. The cookies are much hotter than the tray.

Answer 1

1. If the Temperature raises while heating this means that there can't be a face change happening, face changes occur at constant T. This rules out melting and boiling too, they both are face changes. Also we can state that Temperature is a macroscopic indicator of the level of Kinetic Energy of the microscopic particles, and as T increases KE of particles increases. Therefore b is the right answer

2. If after a long time the two faces are still coexisting they must be at the same temperature, and this has to be zero, otherwise there wouldn't be ice present.Therefore b is the right answer

3. Thermal equilibrium means that the objects in contact have the same T, and there is no longer a flow of heat between them, regardless of the internal energy this objects may poses. Besides heat and work are not state properties so it's not a form of energy that the object can have at a given state, but rather something it can give or take during a defined process. Therefore c is correct

4. Heat capacity is defined as the amount of heat we need to provide to an object in order to raise its temperature by 1 degree. If we provide the same amount of heat to 1g of water and to1 kg of water we see that the temperature increase is a thousand times greater for 1g. If we provide the same amount of heat to a certain mass o water and to the same mass of a rock, we see that the temperature increase is greater for the water. So heat depends on the mass and the material (initial temperature of the object doesn't matter) therefore correct answer is a

5. Heat engines convert thermal energy to mechanical energy by taking advantage of the temperature gradient between a hot sink and a cold sing. They use a working substance which goes from a high T to low T, generating work and transferring heat to the cold sink. Therefore correct is b

6. The temperature gradient is the same for the cookies and for the tray (oven temperature to room temperature), then the heat flow is the same initially. If temperature decreases more for the tray this must mean that the tray has a greater heat capacity. Therefore the correct answer is a