A student found that 3 grams of ammonia gas formed 3 grams of solid ammonia when the temperature was lowered enough. Why did the solid ammonia and the ammonia gas have the same
mass?

The mass of a substance is constant according to the law of conservation of mass.

Explanation:

According to the law of conservation of mass, matter can never be created or destroyed in a chemical reaction, even though it may undergo change from one physical state to another.

This means that in an isolated or closed system, the mass of matter will always be the same irrespective of the type of change that matter undergoes. This is so because, the mass of a substance is a measure of the quantity of matter in that substance and is constant. The number of particles does not change during a change of state, only their spacing and arrangement. In solid ammonia, the particles are more compact and arranged, whereas in gaseous ammonia, they are more randomly spaced out.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.