2a) Someone finds teo bottles without labels. Both are white solids.
One of the white solids turns directly from a solid to a gas on heating. What is this type of change called?
b) The other solid turns yellow on heating. On cooling it turns white again. What might this solid be? (give it's name)?
c)Would you describe the effect of heat on the white powders as a physical change or a chemical change? Give one reason for your answer.
Can I suggest that you post some answers for us to comment on. We are not here to do the home work for you.
Incidently there are two answers to 2a) a strict physical chemists answer and a more general answer.
2a. A substance changing directly from a solid to a gas is called sublimation.
b. Several possibilities. You probably have the name in your notes or in the lab manual. Look at what experiment you are conducting (or getting ready to conduct).
c. The sublimation change is a physical change. You need to know the answer to b before answering this one.
A physcial chemist would refer to the process in a) as evaporation. Altough more commonly it is called sublimination. Sublimination has a particular definition in that it requires the material to go back to the solid phase in the same way distillation goes from the liquid phase to the gas phase and back to the liquid phase.
a) The type of change where a solid directly turns into a gas on heating is called sublimation. In this process, the solid skips the liquid phase and goes directly to the gas phase.
b) The solid that turns yellow on heating and then white again on cooling is most likely iodine. Iodine is a nonmetallic element that sublimes when heated, and the vapor has a yellow color. When the gaseous iodine condenses upon cooling, it forms a white solid again.
c) The effect of heat on the white powders can be described as a physical change. This is because in both cases (sublimation and temporary color change), the alteration in the appearance or physical state of the substances is reversible, without any change in their chemical composition. In sublimation, the white solid is simply converting directly to a gas, and upon cooling, it will revert back to its original form. Similarly, the yellow color change in the other solid is temporary and can be reversed by cooling.