What happens to the heat that is being added to the beaker during the phase change?

The heat supplied during the phase change leads to the change in molecular structures, crystal structures of the substance.

During a phase change, either melting or boiling, the temperature of the substance remains fixed. This is because, if the substance was a solid, then it needs energy for destruction of the crystal structure and gain the particular molecular conformation to be a liquid. Similarly in case of a liquid boiling, it needs energy to overcome the molecular cohesive and adhesive forces to leave the liquid state and become a gas.

So when even after supplying heat the temperature of a system doesn't rise, that means the system is performing equal amount of work. That's why the temperature doesn't increase. This is mentioned as the latent heats in physics.

The heat is used for breaking the bonds of the molecules in the beaker.

Explanation:

In the beaker liquid phase is there suppose it is water the heat provided will be used up in breaking the bond and overcoming the forces that keep the molecules together.

The temperature does not change during phase change.

The heat energy provided will cause the molecules to be far apart.

The added heat will be stored as potential energy.

1. the question asks the most appropriate, which seems to rule out "all of the above." your choice appears to be the correct one.

2. the protocol described is good for identifying correlation, but not cause and effect. for cause/effect, you need to devise a protocol that will assign the treatment (or not) to groups that have essentially the same "demographics" with respect to all the other variables. your choice regarding control group seems appropriate. random assignment of treatment (choice d) may be appropriate also. (i think you can argue that b and d are just different descriptions of the same method.)

3. d will randomize the birds, but may not guarantee there are 10 in each group. e will do both, so seems the better choice.

comment on question 2

based on the problem statement, it seems clear that confident, attentive drivers are more likely to use daytime running lights. so, the protocol might need to be devised in such a way that the lights would be turned on or off without the driver's knowledge. (an attentive driver will figure it out.) assigning a confident, attentive driver to a group required to drive without running lights might mess with his/her confidence and attentiveness. you don't want your experiment to do that. (nor do you want the experiment to subject a driver to greater risk of accident as a consequence of driving without running lights.) experiments involving human safety are always problematic.

b.final