Refer to Figure 11.33 to answer each question. a. A sample...

Refer to Figure 11.33 to answer each question. a. A sample of steam begins on the line segment labeled 5 on the graph. Is heat absorbed or released in moving from the line segment labeled 5 to the line segment labeled 3? What is the sign of q for this change? b. In moving from left to right along the line segment labeled 2 on the graph, heat is absorbed, but the temperature remains constant. Where does the heat go? c. How would the graph change if it were for another substance (other than water)?

Refer to Figure 11.33 to answer each question.
a. A sample of steam begins on the line segment labeled 5 on the graph. Is heat absorbed or released in moving from the line segment labeled 5 to the line segment labeled 3? What is the sign of q for this change?
b. In moving from left to right along the line segment labeled 2 on the graph, heat is absorbed, but the temperature remains constant. Where does the heat go?
c. How would the graph change if it were for another substance (other than water)?

Key Concepts

Latent Heat

Latent heat refers to the energy required to change a substance from one phase to another at a constant temperature. This concept explains why, during a phase change such as melting or condensation, heat is absorbed or released without a change in temperature, as the energy is used to overcome intermolecular forces rather than to increase kinetic energy.

Phase Changes

Phase changes involve the transformation of a substance from one state of matter to another (e.g., liquid to gas or gas to liquid). During these transitions, despite heat transfer taking place, the temperature remains constant. This is because the absorbed or released energy is used entirely for breaking or forming intermolecular bonds, rather than altering the thermal motion of particles.

Heat Transfer and Sign Convention

Understanding heat transfer includes interpreting the sign of q, where a positive value indicates that heat is absorbed (endothermic process) and a negative value indicates that heat is released (exothermic process). This concept is essential when analyzing processes in thermodynamic graphs, particularly during phase transitions.

Phase Diagrams

Phase diagrams graphically represent the conditions of temperature and pressure under which distinct phases of a substance exist. These diagrams help in identifying regions of phase stability, delineating between phase transitions where latent heat is absorbed or released, and showing the influence of substance-specific properties on its thermodynamic behavior.

Transcript

00:02 Okay, this is chapter 11, section problem 104.

00:05 And it asks us to refer to figure 11 .3 to answer these questions, and i have that right here.

00:13 So this is the heating curve of water, and we can see that they labeled the different regions of this heating curve as 1, 2, 3, 4, and 5, and that relates to the different regions.

00:27 So ice, and then we have the melting of ice, which is fusion.

00:31 Then we have the heating of the liquid water, we have the boiling or vaporization, and then we have number five is the heating of the gaseous vapor.

00:44 So a asks us, a sample of steam begins on the line segment labeled five on the graph.

00:51 Okay, over here.

00:53 Is heat absorbed or released in moving from the line segment labeled five to the line segment labeled three? and what's the sign of a cue for that change? so in addition to the graph literally saying that heat is added moving from left to right, which would mean that the reverse of that moving from right to left would mean that heat is released.

01:16 We know that, you know, when you're going down in temperature, your molecules of water are losing kinetic energy.

01:26 So they have to be released, generally speaking.

01:30 And what's the sign of that change? so it's going to be released.

01:38 And the sign is a negative change in q.

01:43 So when we're talking about q, that's the internal energy that those molecules have.

01:52 So it's releasing that energy from inside those molecules to the solution or to the surrounding.

01:59 And it's giving up its energy and therefore it's negative change in the q.

02:04 Okay.

02:04 B, in moving from left to right along the line segment, labeled two on a graph, heat is absorbed, which confirms our answer from a.

02:13 But the temperature remains constant.

02:15 Where does the heat go? okay, so it is true that when you're melting ice, the temperature doesn't change until you have completed the conversion from solid to liquid.

02:28 And that energy goes really into disrupting the stabilization provided by the crystal lattice structure.

02:35 So it goes to breaking that stability provided from the solid...

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