1. which of the following is an example of a physical change to matter?
a. rusting
b. digestion
c. freezing
2. which of the following is an example of a chemical change?
a. melting a stick of butter
b. dissolving salt in water
c. using magnesium to displace hydrogen gas from water

Asubstance is held in an open container. its particles move past one another at random speeds but do not leave the container. heat is removed from the system, and the particles slow down. when enough heat is removed, the particles no longer have enough speed to overcome the weak attractive forces between them. when this happens, the substance enters its solid state. the process described above is known as .

In which of the following phases of matter do molecules have the highest amount of energy? a. liquid b. gel c. solid d. gas

An engineer decides to use a slightly weaker material rather than a stronger material, since she knows that the stronger material can break suddenly. this is an example of what? a choosing a material that will show warning before it fails b using composite materials that combine strength c using a material for multiple applications d using design techniques that increase efficiency and reduce cost