Math Problem Statement

A mixture of helium and hydrogen gas is compressed from a volume of

65.0L

to a volume of

23.0L

, while the pressure is held constant at

63.0atm

. Calculate the work done on the gas mixture. Be sure your answer has the correct sign (positive or negative) and the correct number of significant digits.

kJ

Solution

To calculate the work done on a gas during compression at constant pressure, we use the formula:

W=PΔVW = -P \Delta V

where:

  • WW is the work done,
  • PP is the constant pressure,
  • ΔV\Delta V is the change in volume (VfinalVinitialV_{\text{final}} - V_{\text{initial}}).

Given:

  • Initial volume, Vinitial=65.0LV_{\text{initial}} = 65.0 \, \text{L}
  • Final volume, Vfinal=23.0LV_{\text{final}} = 23.0 \, \text{L}
  • Pressure, P=63.0atmP = 63.0 \, \text{atm}

Step 1: Calculate the Change in Volume

ΔV=VfinalVinitial=23.0L65.0L=42.0L\Delta V = V_{\text{final}} - V_{\text{initial}} = 23.0 \, \text{L} - 65.0 \, \text{L} = -42.0 \, \text{L}

Step 2: Calculate Work in Liter-atm

Since W=PΔVW = -P \Delta V: W=(63.0atm)(42.0L)=2646L\cdotpatmW = -(63.0 \, \text{atm})(-42.0 \, \text{L}) = 2646 \, \text{L·atm}

Step 3: Convert Work to kJ

To convert from L·atm to kJ, use the conversion factor 1L\cdotpatm=0.101325kJ1 \, \text{L·atm} = 0.101325 \, \text{kJ}: W=2646L\cdotpatm×0.101325kJ/L\cdotpatm=268.12kJW = 2646 \, \text{L·atm} \times 0.101325 \, \text{kJ/L·atm} = 268.12 \, \text{kJ}

Step 4: Determine the Sign and Significant Figures

Since the gas is being compressed, work is done on the gas, meaning WW should be positive.

With three significant figures in the given values, we round to: W=268kJW = 268 \, \text{kJ}

Final Answer

The work done on the gas mixture is: 268kJ\boxed{268 \, \text{kJ}}

Would you like further details on the calculation steps, or do you have any questions?


Here are five related questions for practice:

  1. What would the work done be if the gas expanded instead of being compressed?
  2. How does changing the pressure affect the work done in a similar process?
  3. What if the initial volume were increased to 100.0 L—how would that change the result?
  4. How is the sign of work determined in thermodynamic processes?
  5. How would we calculate work if pressure were not constant?

Tip: Always double-check the units and the sign conventions for work in thermodynamics, as they can vary with different processes and setups.

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Math Problem Analysis

Mathematical Concepts

Thermodynamics
Work in Physics
Significant Figures

Formulas

W = -P ΔV
ΔV = V_final - V_initial
1 L·atm = 0.101325 kJ

Theorems

Work-Energy Principle in Thermodynamics

Suitable Grade Level

Grades 11-12