Calculate ΔE for each of the following. a. q=-47 kJ, w=+88 kJ b. q=+82 kJ, w=-47 kJ c. q=+47

Calculate ΔE for each of the following. a. q=-47 kJ, w=+88...

Calculate $\Delta E$ for each of the following.
a. $q=-47 \mathrm{~kJ}, w=+88 \mathrm{~kJ}$
b. $q=+82 \mathrm{~kJ}, w=-47 \mathrm{~kJ}$
c. $q=+47 \mathrm{~kJ}, w=0$
d. In which of these cases do the surroundings do work on the system?

Key Concepts

Sign Conventions

The proper assignment of positive and negative signs to heat and work is crucial for correctly applying the first law of thermodynamics. Positive work indicates energy being transferred to the system by the surroundings, while negative work indicates the system doing work on the surroundings. This concept helps determine the direction of energy flow in a thermodynamic process.

Work (w)

Work in thermodynamics is the energy transferred when a force moves the boundary of a system, such as during compression or expansion. It is essential to distinguish between work done on the system (positive) and work done by the system (negative), which directly affects the internal energy change.

Heat Transfer (q)

Heat transfer represents the energy exchanged as a result of a temperature difference between the system and its surroundings. The sign of q is positive when heat is absorbed by the system (endothermic process) and negative when heat is released (exothermic process).

First Law of Thermodynamics

This fundamental principle states that the change in a system's internal energy (?E) is equal to the heat added to the system (q) plus the work done on the system (w). It highlights the conservation of energy and provides the basic equation ?E = q + w for analyzing thermodynamic processes.

Transcript

00:01 All right, so this question asks, given the following some questions, we have a, b and c with the respective q and respective w for each one.

00:13 They want us to calculate the change in energy of the particular system, and so we need to know the main formula.

00:21 The main formula is the change in energy, which i have on the right hand side.

00:25 Delta e equals q plus w, where q equals heat transfer in her out and then work is work done on the system or work done by the system.

00:39 So on the left hand side, i have the main equation.

00:41 I don't have the delta.

00:43 I wrote that on the right.

00:44 We have a negative que indicates heat out of the system.

00:50 Positive q means heat into the system, and then we have a negative w means workout plus w means work is done on the system or work is going in.

01:01 So we're following the sign convention where negative typically means out and then positive means it, whether it's heat, energy or work energy.

01:11 And then we can calculate by adding those two together with the overall energy changes in that particular system and following the same plus or minus convention for final results will have dealt is positively.

01:26 No, overall energy is going in.

01:28 And if we have a delta that's negative.

01:31 Will have energy going out of the system.

01:34 Okay, so we'll go and start with the 1st 1 they give us in a letter.

01:38 A.

01:39 They say that they give us a queue of negative 47 killed, jules, and i'll go ahead and just leave out the killer.

01:48 Jules, we don't need that.

01:51 Put that on our final answer.

01:52 47 killed jules negative.

01:55 And then we have positive 88 for the work.

02:00 Okay, so ultimately, that's gonna give us positive...