Question

1.Which phrase best describes heat?

A.the energy that an object has as a result of its temperature

B.the average translational kinetic energy of the particles in an object

C.the energy transferred between objects at different temperatures

D.the total amount of energy possessed by the particles in an object

2.In an isolated system, two copper bars at different temperatures transfer energy until both are at the same temperature. How would the transfer of energy be different if the bars were in an open system?

A.Energy transfer would occur only between the copper bars.

B.Energy transfer would occur between the copper bars and the surroundings.

C.No energy transfer would occur between the copper bars or the surroundings.

D.Energy transfer would occur only with the surroundings.

3.What happens when carbon dioxide at 74°C is placed in thermal contact with water at 14°C? CHOOSE ALL THAT APPLY

Energy leaves the carbon dioxide and enters the water.

The water gets hotter than the carbon dioxide.

The temperatures of the two substances equalize.

Both the water and the carbon dioxide decrease in temperature.

The water stays colder than the carbon dioxide.

4.What is the mass of a titanium alloy that has a heat of fusion of 422.5 joules/gram and requires 2,960 joules of energy to melt completely?

Use the formula Q = mH_f.

A.0.143 g

B.1.43 g

C.7.01 g

D.7.81 g

Answer 1

1) The term Heat makes sense only if there is a temperature gradient existing which means that heat is the energy flowing from one object to another by virtue of the temperature difference between the objects. Thus, the correct option is C.the energy transferred between objects at different temperatures.

2)

The basic point of an isolated system is that there is no exchange of energy in any form outside the system which means all energy exchange takes place within the system. If the copper bars were in an open system, there could be exchange of Energy as well as Mass with the surroundings. Thus apart from the energy transfer between the copper bars, there would be energy exchange with the surroundings too.

Option B.Energy transfer would occur between the copper bars and the surroundings.

3)

Since carbon dioxide is at a higher temperature initially than water, Carbon dioxide would loose energy and water would gain the energy lost by CO₂. This energy exchange would take place till both are in thermal euilibrium or at the same temperature.

Thus the correct options are: 1)Energy leaves the carbon dioxide and enters the water.

2)The temperatures of the two substances equalize.

4)

Q = m x H_f

Q is the energy required, m is the mass and H_f is the heat of fusion.

m = Q/H_f = 2960 joules/ 422.5 joules/gram = 7.01 g

Thus option C. 7.01 g