Question

Scenes A–D represent atomic-scale views of different samples of substances:

​​​​​​​                              ​​​​​​​​​​​​​​​​​​​​​​​​​​​

(a) Under one set of conditions, the substances in A and B mix, and the result is depicted in C. Does this represent a chemical or a physical change?

(b) Under a second set of conditions, the same substances mix, and the result is depicted in D. Does this represent a chemical or a physical change?

(c) Under a third set of conditions, the sample depicted in C changes to that in D. Does this represent a chemical or a physical change?

(d) After the change in part (c) has occurred, does the sample have different chemical properties? Physical properties?

Answer 1

Solution

a) First of all, let`s look at the substances we have at the beginning. We have gas molecules (red molecules) and solid molecules (blue molecules). The result of them interacting, in this case, is depicted as a compound that consists of both of them.

Chemical change by definition is a change in which a substance or mixture of substances is converted into a new substance.

We can conclude that this is a chemical change because the interaction resulted in the formation of a new molecule.

We also have a formation of chemical bonds between red and blue substances. We know that the reaction is chemical because the formed substance is a compound formed from both substances we had at the beginning and it is moving in the form of Brownian motion.

b) First of all, let's look at the substances we have at the beginning.

We have gas molecules (red molecules) and solid molecules (blue molecules). The result of them interacting in this case is depicted as compound that consists of both of them but it is in solid-state.

Chemical change by definition is a change in which a substance or mixture of substances is converted into a new substance.

We can conclude that this is a chemical change because the interaction resulted in compound that is a mixture of both substances we had at the beginning but this time, the newly formed compound is in solid-state opposed to the subtask a) where the new compound was in a gaseous state.

c) First of all, let`s look at the substance we have at the beginning. We have a compound that consists of both red atoms and blue atoms. There is a chemical bond between the atoms in the molecule. The molecule is in a gaseous state.

Physical change is a change in which a substance or mixture of substances are not converted into a new molecule but there is a change in the physical state of at least one substance.

We can conclude that this is a physical change because we have the same compound but in a different state.

To put it simply, no new molecule was created. There was just a change in the state of molecule. It can occur because of the change in temperature, pressure, or a combination of both.

d) The change that occurred in example c) is a physical change.

When a physical change occurs, the chemical properties of the compound stay the same but physical properties change.

a) chemical change

b) chemical change

c) physical change

d) different physical properties