For each of the following processes, indicate whether the signs of ΔS and ΔH are expected to be

step 1 Alright, so here's the problem 88 for chapter 19. And in this question, we're going to decide wh

For each of the following processes, indicate whether the...

For each of the following processes, indicate whether the signs of $\Delta S$ and $\Delta H$ are expected to be positive, negative, or about zero. (a) A solid sublimes. (b) The temperature of a sample of $\mathrm{Co}(s)$ is lowered from $60^{\circ} \mathrm{C}$ to $25^{\circ} \mathrm{C}$. (c) Ethyl alcohol evaporates from a beaker. (d) A diatomic molecule dissociates into atoms. (e) A piece of charcoal is combusted to form $\mathrm{CO}_{2}(g)$ and $\mathrm{H}_{2} \mathrm{O}(g)$.

Key Concepts

Entropy Change (?S)

This concept refers to the measure of disorder or randomness in a system. A positive ?S indicates that the system becomes more disordered (for example, when a solid converts directly to a gas or when a molecule breaks into smaller pieces), whereas a negative ?S indicates a decrease in disorder (such as when a gas condenses into a liquid or a system cools).

Enthalpy Change (?H)

Enthalpy change represents the heat absorbed or released during a process at constant pressure. A positive ?H signifies that the process is endothermic, meaning it requires the absorption of heat from the surroundings, while a negative ?H means the process is exothermic, releasing heat into the surroundings.

Phase Transitions

Phase transitions involve changes between states of matter, such as solids, liquids, and gases. These changes typically involve significant alterations in entropy and enthalpy; for instance, processes like sublimation and evaporation usually increase disorder and are endothermic under standard conditions.

Temperature Effects on Thermodynamic Properties

Temperature plays a crucial role in influencing both enthalpy and entropy. Changes in temperature can affect the amount of heat exchange (enthalpy) and the degree of molecular motion, which in turn alters the system’s disorder (entropy). Lowering the temperature often reduces entropy as molecular motion decreases.

Chemical Reaction Thermodynamics

This concept encompasses the study of energy changes, including both ?H and ?S, in chemical reactions such as bond breaking (dissociation) or bond formation (combustion). The nature of these reactions determines whether the process is endothermic or exothermic and affects the overall disorder of the system based on the number and type of particles formed.

Transcript

00:01 Alright, so here's the problem 88 for chapter 19.

00:03 And in this question, we're going to decide whether delta h and delta s are positive or negative, or about zero for each of the following process.

00:17 Part a, a solid sublimatize.

00:19 So sublimation means a compound goes from solid to its gas phase.

00:26 So solid goes to gas requires absorption of, absorption of heat, and if it absorbs heat, it's an endothermic reaction.

00:43 So delta h is positive.

00:46 Also, there are more degree of freedom in gas compared to solid.

00:51 So the entropy of the system increases, so delta s is also positive.

01:02 Part b, we have temperature of a sample is lowered from 60 to 25.

01:09 So temperature goes from 60 to 25 degrees.

01:14 When temperature cools down, the sample will release heat.

01:20 Releasing heat means it's an exothermic process, and exothermic has delta -h negative.

01:30 Also, by lowering the temperature, the molecules are less movable.

01:36 So the entropy of the system decreases, will have a delta s also negative.