Predict whether the values of q; w; du, and dh are positive, zero, or negative for each of the following processes: (a) melting of ice at 1 atm and 273 k, (b) melting of solid cyclohexane at 1 atm and the normal melting point, (c) reversible isothermal expansion of an ideal gas, and (d) reversible adiabatic expansion of an ideal gas

for (a) and (b); q= positive, w=positive, ∆U= negative, ∆H= positive.

(c) reversible isothermal expansion; q= negative ; w= negative, ∆U= zero, ∆H=zero

(d) adiabatic expansion: q= zero, ∆U= negative, w= negative, ∆H=negative

Explanation: for melting work is done on the system.

For isothermal changes, it occurs at constant temperature. q=∆E-w . At constant temperature, ∆E=0. Therefore q=w.

For adiabatic changes, it occurs such that there is no change in heat between the system and the surroundings. Hence, q=0. Which implies that ∆U= -w

The equation ∆U= -w simply means that in an adiabatic change any work done is at the expence of internal energy. An increase in workdone leads to a decrease in internal energy of a system.

so here we go

atomic mass

239 + 1 = y + 134 + 3 combine like terms

240 = y + 137             subtract 137 from both terms

240 - 137 = y

103 = y

atomic number

94 = z +54 + 0

94 = z + 54               subtract 54 from both sides.

40 = z

answer

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.