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Lesson: Enthalpy and Internal Energy

In this lesson, we will learn how to calculate enthalpy changes from changes in internal energy and changes in volume, at constant pressure.

Worksheet • 4 Questions

Q1:

A 1.50-mole 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 be the enthalpy change ( Ξ” 𝐻 ) of the gas in this process?

Q2:

The standard heat of combustion of solid glucose ( C H O ) 6 1 2 6 at 298 K is Ξ” 𝐻 ( 2 9 8 ) ⦡ c K = βˆ’ 2 8 0 1 kJ/mol. What is the value of Ξ” π‘ˆ ⦡ c , the change in internal energy accompanying the combustion at 298 K and a fixed pressure of 1 bar?

Q3:

Consider the reaction C H C O O H ( ) + ( 1 5 / 2 ) O ( ) 7 C O ( ) + 3 H O ( ) 6 5 2 2 2 s g g l , for which the standard reaction enthalpy is Ξ” 𝐻 = βˆ’ 3 2 2 8 . 2 / ⦡ r k J m o l . Calculate the value of Ξ” π‘ˆ ⦡ r for this reaction and determine whether any thermodynamic work is done on ( 𝑀 > 0 ) or by ( 𝑀 < 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 = 2 9 8 . 1 5 K and 𝑃 = 1 b a r .

  • A Ξ” π‘ˆ = βˆ’ 3 2 2 7 . 0 / ⦡ r k J m o l and 𝑀 < 0
  • B Ξ” π‘ˆ = βˆ’ 3 2 2 7 . 0 / ⦡ r k J m o l and 𝑀 > 0
  • C Ξ” π‘ˆ = βˆ’ 3 2 3 0 . 7 / ⦡ r k J m o l and 𝑀 < 0
  • D Ξ” π‘ˆ = βˆ’ 3 2 2 8 . 2 / ⦡ r k J m o l and 𝑀 = 0
  • E Ξ” π‘ˆ = βˆ’ 3 2 3 0 . 7 / ⦡ r k J m o l and 𝑀 = 0

Q4:

Consider the reaction 2 C ( ) + C l ( ) + 2 F ( ) C F C l C F C l ( ) s g g g 2 2 2 2 , for which the standard reaction enthalpy has a value of Ξ” 𝐻 = βˆ’ 8 9 0 . 4 / ⦡ r k J m o l at a temperature of 298 K. What is the value of Ξ” π‘ˆ ⦡ r for this reaction at 𝑇 = 2 9 8 K ?
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