A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 

1atm

. The cylinder is also submerged in a large insulated water bath. (See sketch at right.)

From previous experiments, this chemical reaction is known to absorb 

274.kJ

 of energy.

The position of the piston is monitored, and it is determined from this data that the system does 

176.kJ

 of work on the piston during the reaction.


Is the reaction exothermic or endothermic?

exothermic

endothermic

Does the temperature of the water bath go up or down?

up

down

neither

Does the piston move in or out?

in

out

neither

Does heat flow into or out of the gas mixture?

in

out

neither

How much heat flows? Be sure your answer has the correct number of significant digits.

kJ




To solve this, let's break down each part step by step:

### 1. Is the reaction exothermic or endothermic?
- The reaction **absorbs** 274 kJ of energy. Since it absorbs energy from the surroundings, the reaction is **endothermic**.

### 2. Does the temperature of the water bath go up or down?
- In an **endothermic reaction**, energy is absorbed from the surroundings, which in this case includes the water bath. This causes the water bath to **cool down**. So, the temperature of the water bath goes **down**.

### 3. Does the piston move in or out?
- The system does 176 kJ of **work on the piston**. When a gas does work, it means the volume of the gas is expanding, causing the piston to move **out**.

### 4. Does heat flow into or out of the gas mixture?
- Since the reaction is endothermic, heat flows **into** the gas mixture from the surroundings.

### 5. How much heat flows?
To calculate the amount of heat (q) that flows into the system, we use the **First Law of Thermodynamics**:

\[
\Delta U = q - w
\]

Where:
- \(\Delta U\) is the change in internal energy, given as 274 kJ (since the reaction absorbs this much energy).
- \(w\) is the work done by the system on the surroundings, which is 176 kJ.

Rearranging the formula to solve for \(q\):

\[
q = \Delta U + w
\]

Substitute the values:

\[
q = 274\ \text{kJ} + 176\ \text{kJ} = 450\ \text{kJ}
\]

So, **450 kJ** of heat flows **into** the system.

---

### Summary of answers:
1. The reaction is **endothermic**.
2. The temperature of the water bath goes **down**.
3. The piston moves **out**.
4. Heat flows **into** the gas mixture.
5. **450 kJ** of heat flows into the system.

---

Would you like further clarification on any of these points?  
Here are five related questions for expanding this concept:
1. What is the difference between an endothermic and an exothermic reaction?
2. How does the First Law of Thermodynamics relate to heat and work?
3. How would the system behave if the pressure were not constant?
4. What factors determine the direction of piston movement in a cylinder?
5. What are some examples of endothermic reactions in real life?

**Tip:** Always keep track of the sign conventions for heat and work in thermodynamics to avoid confusion when applying formulas.

A mixture of gaseous reactants is put into a cylinder, where a chemical reaction turns them into gaseous products. The cylinder has a piston that moves in or out, as necessary, to keep a constant pressure on the mixture of 1atm. The cylinder is also submerged in a large insulated water bath. From previous experiments, this chemical reaction is known to absorb 274 kJ of energy. The position of the piston is monitored, and it is determined from this data that the system does 176 kJ of work on the piston during the reaction. Is the reaction exothermic or endothermic? Does the temperature of the water bath go up or down? Does the piston move in or out? Does heat flow into or out of the gas mixture? How much heat flows?

This thermodynamics problem focuses on a reaction in a constant pressure system where a mixture of gases absorbs 274 kJ of energy and does 176 kJ of work on a piston. Learn to apply the First Law of Thermodynamics and calculate heat flow into the system. Suitable for advanced high school or college-level students.

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