Question

1. For the process H2O(g) → H2O(l) at 105°C the signs on AG, AH, and AS are a)-, t, + b)t, -, - c) +, +, + d) +, t, - e)-, -, - 2. For the process H2O(l) → H2O(s) at -5°C the signs on AG, AH, and AS are a)-, +, + b) +, -, - c) +, +, + d) +, +, - e)-,-,- 3. For the process H2O(s) → H2O(l) at +5°C the signs on AG, AH, and AS are a)-, +, + b) +, -, - c) +, +, + d) +, +, - e)-, -,-

Answer 1

All Three questions are based on the equation:

ΔG = ΔH - T*ΔS

1. b) +,-,-

Reason :

• ΔH is -ve because conversion from gas to liquid means heat is given out by the molecules.  
• ΔS is -ve because conversion from gas to liquid leads to greater stability or orderliness in molecules. As orderliness increase, entropy (S) decrease
• ΔG is +ve since the process is taking place at a higher temperature(105 degree Celcius). From the equation you can understand that for -ve ΔH and -ve ΔS,at higher temperatures, ΔG is +ve. Also you can logically think that conversion of water vapour to liquid water is non-spontaneous above 100 degree celcius.Non spontaneous processes have +ve ΔG

2. e)-,-,-

Reason :

• ΔH is -ve because conversion from liquid to solid means heat is given out by the molecules.  
• ΔS is -ve because conversion from liquid to solid leads to greater stability or orderliness in molecules. As orderliness increase, entropy (S) decrease
• ΔG is -ve since the process is taking place at a very low temperature(-5 degree Celcius). From the equation you can understand that for -ve ΔH and -ve ΔS,at lower temperatures, ΔG is -ve. Also you can logically think that conversion of water to ice is a spontaneous process below 0 degree celcius.Spontaneous processes have -ve ΔG

3. a)-,+,+

• ΔH is +ve because conversion from solid to liquid means heat is taken up by the molecules.  
• ΔS is +ve because conversion from solid to liquid leads to greater disorderliness of molecules. As disorderliness increase, entropy (S) increase.
• Conversion of  ice to water is a spontaneous process above 0 degree celcius.Spontaneous processes have -ve ΔG