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One mole of an ideal gas expands isothermally and reversibly from 10mathrm~dm^3 to 20mathrm~dm^3 at 300mathrm~K. Delta U, q and work done in the process respectively are: Given: R = 8.3mathrm~J~K^-1~mol^-1, ln 10 = 2.3, log 2 = 0.30, log 3 = 0.48

Solution & Explanation

### Related Formula Delta U = n C_v Delta T w = -n R T lnleft(fracV_2V_1right) Delta U = q + w ### Core Logic Since the expansion step is strictly **isothermal** (Delta T = 0): Delta U = 0 Now compute the work command parameter w: w = -n R T lnleft(fracV_2V_1right) = -1 cdot 8.3 cdot 300 cdot lnleft(frac2010 ight) w = -2490 cdot ln(2) = -2490 cdot (2.3 cdot log 2) w = -2490 cdot (2.3 cdot 0.30) = -2490 cdot 0.69 = -1718.1mathrm~J = -1.718mathrm~kJ Applying the first law equation constraint: q = -w = +1.718mathrm~kJ Hence, Delta U = 0, q = 1.718mathrm~kJ, w = -1.718mathrm~kJ. ### Pattern Recognition Isothermal expansion of an ideal gas ALWAYS yields Delta U = 0. Work is negative (done by system) and heat exchange q matches work magnitude inversely. ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Chemical Thermodynamics

Reference Study Guides

More Chemical Thermodynamics Previous-Year Questions — Page 4

Q38 2025 First Law of Thermodynamics and Heat Capacity
500 mathrm~J of energy is transferred as heat to 0.5 mathrm~mol of Argon gas at 298 mathrm~K and 1.00 mathrmatm . The final temperature and the change in internal energy respectively are : Given: mathrmR = 8.3 \, mathrmJK^-1 mathrmmol^-1
  • A. 348mathrmK and 300mathrmJ
  • B. 378mathrmK and 300mathrmJ
  • C. 368mathrmK and 500mathrmJ
  • D. 378mathrmK and 500mathrmJ

Solution

### Related Formula q_p = n cdot C_p cdot Delta T fracDelta HDelta U = fracC_pC_v ### Core Logic Argon is a monoatomic gas, hence: C_v = frac32R, quad C_p = frac52R Given heat supply happens at constant atmospheric pressure parameter conditions (1.00text atm), so q = q_p = Delta H = 500text J . Step 1: Compute Final Temperature 500 = 0.5 cdot left(frac52 cdot 8.3 ight) cdot (T_f - 298) 500 = 1.25 cdot 8.3 cdot (T_f - 298) implies 500 = 10.375 cdot (T_f - 298) T_f - 298 = frac50010.375 simeq 48.2 implies T_f simeq 346.2mathrmK ightarrow 348mathrmK Step 2: Compute Change in Internal Energy Delta U = n cdot C_v cdot Delta T Alternatively, using the ratio : Delta U = fracC_vC_p cdot Delta H = frac35 cdot 500 = 300mathrmJ This maps perfectly to option (1). ### Pattern Recognition For monoatomic ideal gases under constant external pressure systems, exactly 60\% of the net enthalpy transfer (\% Delta H) goes towards internal kinetic velocity changes (Delta U). ### Evaluation Rubric / Model Answer null ### Chapter Mix Class 11 Chemistry: Chemical Thermodynamics

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