It is a true fact that ionic crystals are excellent insulators and can hold a large amount of heat before melting or boiling. The correct option among the two options that are given in the question is the first option. Salt is a great example of ionic crystals and we know that it takes a huge amount of time to melt or boil.
Lets do process of elimination!
A. Breaking glass - That is a psychical change because if you break it, it is still glass. It didn't change to another substance.
B. Melting ice on a windshield - During the melting process, there is no chemical change, and therefore, no new substance is created.
C. Burning gasoline - When gas burns it usually combines with oxygen to give carbon dioxide, water etc. It is a chemical change.
D. Denting a bumper - The bumper is still a bumper, only thing is it has a dent in it. The properties did not change, meaning no chemical change.
Answer:
2-4 mm height of capillary tube.
Explanation:
Sample should be around 2-4 mm in height.
It should be packed well so that it does not have air packets that caues the lowering of melting point.
If you take greater amount, then there will be needed more heat, resulting a wide range of melting point.
We write DE = q+w, where DE is the internal energy change and q and w are heat and work, respectively.
(b)Under what conditions will the quantities q and w be negative numbers?
q is negative when heat flows from the system to the surroundings, and w is negative when the system does work on the surroundings.
As an aside: In applying the first law, do we need to measure the internal energy of a system? Explain.
The absolute internal energy of a system cannot be measured, at least in any practical sense. The internal energy encompasses the kinetic energy of all moving particles in the system, including subatomic particles, as well as the electrostatic potential energies between all these particles. We can measure the change in internal energy (DE) as the result of a chemical or physical change, but we cannot determine the absolute internal energy of either the initial or the final state. The first law allows us to calculate the change in internal energy during a transformation by calculating the heat and work exchanged between the system and its surroundings.