A gas is confined to a cylinder under constant atmospheric
press...

Question

A gas is confined to a cylinder under constant atmospheric 
pressure, as illustrated in Figure 5.4. When 0.49 kJ of heat is 
added to the gas, it expands and does 214 J of work on the 
surroundings. What are the values of H and E for this 
process?

Accepted Answer

Welcome back everyone. A gas is contained in a cylinder fitted with a movable piston and held at a constant pressure. When 315 jewels of work is done on the system, the volume of the gas decreases and .640 kg joules of heat is released into the surroundings, calculate the entropy change and change in internal energy for the system. So let's begin by first recalling how internal energy change of the system is calculated and recall that we would take the sum between our variable for heat which is represented as Q. To our variable for work represented as W. Recall that for each of these variables are units can either be expressed in terms of jewels or killed jules. Now let's define what our system is. The prompt tells us that once work is done on the system the volume of the gas decreases. And that means that our system in this prompt is the gas. And so the surroundings would be what contains this gas, which is our cylinder. And specifically the movable piston. Within this cylinder is the boundary separating our system from the surroundings. So let's go back to the prompt and understand what are variables for Q. And W actually are. The prompt tells us that 315 jewels of work is done on the system. And so that means that our piston exerts a force on the gas. And so work is done on the system Meaning that our sign for W is going to be positive. And so we would say that work is equal to positive. 315 jewels. Now let's focus on our variable for heat expresses Q. So we have according to the prompt .640 kg of heat released into the surroundings. And so we would say that the system loses heat, which is why the volume of the gas decreases. And so we would say that Q. is equal to negative .640 killer jules. Now we want to make sure our units are matching. So let's go ahead and convert our term for work from jewels to kill jules. So we'll have jewels in the denominator and kill jewels in the numerator. And recall that our prefix kilo tells us that we have for one kg jewel and equivalents of 10 to the negative third. Kill jules. So canceling out jewels were left with kilo jewels for our unit of work and this gives us point were positive 100.0.3 kila jewels of work done to our system. So now that we understand our variables Q. And w. Let's go back to calculating our internal energy change for the system. So we would say that Q. Which we determined as negative .640 kg jewels Is added to the work done to our system, which we determined to be positive as 300 or .315. Sorry, kill it jules. And so taking this some we would find our internal energy of the system equal to a value of negative 0. 25 kg joules. And this is a five here. Kill it jules. So this would be our first answer. Now, going back to the prompt, which states that the piston and the cylinder containing the gas are held at constant pressure. So recall that if the system is held at constant pressure, we can say that heat is equivalent to our entropy change. And so we would say that Our heat is or sorry, our entropy change of the system, Delta H is equal to also negative 0.640 killer whales. And that would be our second final answer. So overall we can conclude that overall our system gains energy initially through the mechanical force of work which was done by the piston on our system. And then from there our system loses energy as heat being the volume of the gas decreasing. So what's highlighted in yellow are our final answers corresponding to choice A in the multiple choice. I hope that everything argued was clear. If you have any questions, please leave them down below and I'll see everyone in the next practice video

A gas is confined to a cylinder under constant atmospheric pressure, as illustrated in Figure 5.4. When 0.49 kJ of heat is added to the gas, it expands and does 214 J of work on the surroundings. What are the values of H and E for this process?

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