The accompanying diagram shows how entropy varies with temperature for a substance that is a gas at the highest temperature shown. (c) If this substance is a perfect crystal at T = 0 K, what is the value of S at this temperature?

Video transcript

Welcome back everyone consider the following graph showing the change in entropy of a perfect crystal with temperature. The substances in gaseous form at the highest temperature, which of the statements below is true regarding the substance. And so we would observe at the highest temperature, we have a gaseous form of our crystal and we also have a will say positive sign of entropy, which would make sense since we understand that our gaseous molecules have a great degree of motion associated with an increase in kinetic energy influenced by the high temperatures. Looking at our answer choices we're comparing when the temperature is equal to zero kelvin, how that influences entropy. And so we want to consider that the prompt mentions that we have a perfect crystal and because we have a perfect crystal, our atoms are highly ordered and thus the molecule has no randomness slash disorder or entropy. This is only possible because we have a perfect crystal with a very organized molecular arrangement. And due to this lack of disorder in our arrangement of our perfect crystal molecular structure, we therefore have no random motion of our crystal perfect crystal molecules and with no random motion, there is therefore a lack of increase of entropy. And so really entropy is equal to zero. This would make sense since our temperature is at zero and therefore there's lack of thermal energy to influence the motion of our perfect crystal molecular structure. So based on what we've outlined, we can confirm that the only correct answer choice to complete this example is going to be choice B, which states that when the temperature is equal to zero, our entropy change is also, or entropy value is also equal to zero. So B is our final answer. I hope that what I went through was helpful. But if you have any questions, just let us know and I'll see everyone in the next video.