Explain why water spontaneously freezes to form ice below 0 ^∘ C even though the entropy of the

Explain why water spontaneously freezes to form ice below 0...

Key Concepts

Temperature Dependence in Thermodynamics

The temperature influence in the Gibbs free energy equation (G = H - TS) is crucial in determining spontaneity. At temperatures below 0°C, the term T?S (which is negative when entropy decreases) becomes small enough that the large negative change in enthalpy dominates, resulting in a negative ?G. Conversely, above 0°C, the T?S term is larger and offsets the enthalpy benefit, making the overall free energy change positive and the freezing process non-spontaneous.

Entropy

Entropy quantifies the degree of disorder in a system. When water freezes, its molecules become more orderly, resulting in a decrease in entropy. Although a decrease in entropy tends to oppose spontaneity, in the case of water freezing below 0°C, the substantial enthalpy decrease (release of heat) compensates for this loss of disorder, thereby allowing the process to be thermodynamically favorable.

Gibbs Free Energy

Gibbs free energy represents the balance between enthalpy and entropy (given by the formula G = H - TS), and it determines whether a process is spontaneous. A process will occur spontaneously if the change in Gibbs free energy (?G) is negative. In the context of water freezing, even though the entropy decreases (which would normally oppose spontaneity), the exothermic release of heat (a decrease in enthalpy) overcomes the entropy loss below 0°C, leading to a negative ?G and making the freezing process spontaneous.

Enthalpy

Enthalpy is a measure of the total heat content of a system. During the freezing of water, the formation of hydrogen bonds and the ordering of molecules lead to the release of latent heat. This release of energy results in a significant decrease in enthalpy, which drives the overall process by compensating for the decrease in entropy observed when water turns into ice.

Transcript

00:01 Explain what weather is spontaneously freeze to form ice below 0 degrees celsius, even though entropy of the water decreased during the state transition.

00:12 Why is the freezing of water is not spontaneous above 0 degrees celsius? to solve for this, we want to understand what is spontaneous and what is how to do with entropy.

00:23 So for this question, we're going to say spontaneous.

00:26 To be spontaneous, entropy, or i'm going to use.

00:30 S, in this case, delta s need to be positive.

00:34 We also need to know the definition of delta s.

00:37 What does that mean? delta s is going to be equal to the delta s of the system plus delta s of the surrounding.

00:53 Okay.

00:55 So in this case, the question is saying the freeings of the water, right? the freezing, the add -all water freezing, which is going from the liquid to the solid, is entropy -wise is decreasing, right? entropy is decreasing.

01:12 That's what it is saying.

01:13 So what is that saying? what is it saying is delta as of the system is negative.

01:22 Okay, so that's what i was saying.

01:24 So freezing water, water entropy is negative.

01:27 So how exactly it is going to be? spontaneous.

01:30 Well, it is spontaneous because delta s of the universe is positive.

01:38 Okay, so how is this possible? well, let's see.

01:41 Delta s of system in this case is negative.

01:44 But we're going to add it with some positive value, right? the surrounding is positive value.

01:50 If the surrounding positive value, right, is big enough, bigger than this, then then my delta s of the universe could be positive.

02:07 And if delta s of universe is positive, then it's going to be spontaneous.

02:12 So let's see how exactly that could happen.

02:14 To solve for it, you has actually s of the system.

02:20 I'm just going to write it as system plus as of the surrounding.

02:28 Okay.

02:29 So as of the system, as we already said, it's got to be negative.

02:32 So you're going to say negative plus we said this is positive.

02:37 But what is the as of the surrounding? as of the surrounding can be solved by doing this...

Please give Ace some feedback