Aballoon filled with 39.1 moles of helium has a volume of 876 l at 0.0'c and 1.00 atm pressure. the temperature of the balloon is increased to 38.0'c as it expands to a volume of 998 l, the pressure remaining constant. calculate q, w, and #e for the helium in the balloon. (the molar heat capacity for helium gas is 20.8 j/°c # mol.)

Q = 30.90 kJ, W = 12.36 kJ, ΔE = 18.54 kJ.

Explanation:

The expansion is happening at constant pressure without a phase change, thus, the heat can be calculated by:

Q = n*c*ΔT

Where n is the number of moles, c is the molar heat capacity, and ΔT is the temperature variation (final - initial), thus:

Q = 39.1*20.8*(38.0 - 0.0)

Q = 30904.64 J

Q = 30.90 kJ

The work done by a expansion at constant pressure is:

W = P*ΔV

Where P is the pressure (1 atm = 101325 Pa), and ΔV the volume variation (final - initial). Vfinal = 998 L = 0.998m³, Vinitial = 876 L = 0.876 m³.

W = 101325*(0.998 - 0.876)

W = 12361.65 J

W = 12.36 kJ

By the first law of the thermodynamics, the variation of the internal energy ΔE is:

ΔE = Q - W

ΔE = 30.90 - 12.36

ΔE = 18.54 kJ

definition

                    entropy is a measure of the randomness or the extent of disorder of a chemical process.

                      enthalpy is a measure of the heat change of a reaction occurring at a constant pressure.

measurement units:

                        entropy is measured in joule per kelvin (jk⁻¹)   whereas enthalpy is measured in joule per mole (jmol⁻¹)

requirements:

                            entropy has no requirements or limits, and its change is measured by the division between the heat change of the chemical process and the temperature.

                              in contrast, enthalpy can only be related to the heat change of the reaction under standard conditions.