Calculate the entropy change of the universe (in J/K) when 43.4 g of ethanol vapor is condensed in a laboratory at 20.4 oC. Report your answer in scientific notation to three significant figures.
If something is condensed, does that mean the system gaines heat, or the surroundings gain heat?
Also, would I use enthalpy of fusion or enthapy of vaporization?
You would use the heat of vaporization. And if something is condensed, that means it gives off heat so the universe will gain it.
You can remember the heat absorbed or heat given off easily if you remember this:
I must ADD heat to water at 100 degrees C in order to turn it into steam. Everyone know that. Therefore, if steam is condensing, it must give off heat.
I must ADD heat to ice to melt it. Everyone knows that. Therefore, if liquid water is freezing to ice, it must give off heat.
You may also turn these into equations.
H2O(liquid) + heat ==> H2O(gas)
This shows we add heat to go from liquid water to steam (endothermic). Reverse the equation and it shows heat being given off (exothermic) for condensation.
H2O(ice) + heat ==> H2O(liquid)
This shows we add heat to ice to melt it (endothermic). Reverse the equation and it shows heat is given off when we freeze liquid water (exothermic).
It may be a little tough to think of freezing water as exothermic but the equation helps get it correct.
When a substance undergoes condensation, it means that it changes from the gaseous phase to the liquid phase. During condensation, heat is released by the substance, which means that the surroundings gain heat. Therefore, in this case, the surroundings gain heat when ethanol vapor is condensed in the laboratory.
To calculate the entropy change of the universe, we need to consider both the system (43.4 g of ethanol vapor) and the surroundings (the laboratory). The entropy change of the universe can be calculated using the equation:
ΔS_universe = ΔS_system + ΔS_surroundings
Now let's focus on the system, which is the condensation of ethanol vapor. To calculate the entropy change of the system, we can use the equation:
ΔS_system = n * ΔS_vap
Here, n represents the number of moles of the substance, and ΔS_vap is the molar entropy change during vaporization. Since we are given the mass of ethanol vapor, we need to convert it to moles using the molar mass of ethanol (C2H5OH).
To determine which enthalpy change to use, we need to know if the substance undergoes fusion or vaporization. In this case, the substance is ethanol vapor, and it undergoes condensation, which is the process of changing from the gaseous phase to the liquid phase. Therefore, we will use the enthalpy of vaporization.
To carry out the calculation, we also need the molar entropy change (ΔS_vap) of ethanol vaporization. However, this information is not provided in the question. Therefore, we cannot proceed with the calculation without the required ΔS_vap value.