Worksheet: Enthalpy and Internal Energy

In this worksheet, we will practice calculating enthalpy changes from changes in internal energy and changes in volume, at constant pressure.

Q1:

A 1.50 mol sample of an ideal gas at 245 K and a pressure of 0.75 bar is altered by some process that takes it to a state in which its temperature is increased to 295 K and its pressure is increased to 0.90 bar. What will the enthalpy change (Δ𝐻) of the gas in this process be?

Q2:

Consider the shown reaction, for which the standard reaction enthalpy has a value of Δ𝐻=890.4/rkJmol at a temperature of 298 K. 2C()+Cl()+2F()CFClCFCl()sggg2222 What is the value of Δ𝑈r for this reaction at 𝑇=298K?

Q3:

Consider the shown reaction, for which the standard reaction enthalpy is Δ𝐻=3,228.2/rkJmol. CHCOOH()+O()7CO()+3HO()65222sggl152 Calculate the value of Δ𝑈r for this reaction and determine whether any thermodynamic work is done on (𝑤>0) or by (𝑤<0) the reaction system if the reaction is carried out at a constant pressure. Assume that the gases in this reaction exhibit ideal gas behavior at 𝑇=298.15K and 𝑃=1bar.

  • A Δ 𝑈 = 3 , 2 2 8 . 2 / r k J m o l and 𝑤=0
  • B Δ 𝑈 = 3 , 2 3 0 . 7 / r k J m o l and 𝑤<0
  • C Δ 𝑈 = 3 , 2 3 0 . 7 / r k J m o l and 𝑤=0
  • D Δ 𝑈 = 3 , 2 2 7 . 0 / r k J m o l and 𝑤<0
  • E Δ 𝑈 = 3 , 2 2 7 . 0 / r k J m o l and 𝑤>0

Q4:

The standard heat of combustion of solid glucose (CHO)6126 at 298 K is Δ𝐻(298)=2,801/cKkJmol. What is the value of Δ𝑈c, the change in internal energy accompanying the combustion at 298 K and a fixed pressure of 1 bar?

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