Question
Asked Mar 12, 2019
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4.36)  Predict the signs of ΔH, ΔS, and ΔG of the system for the following processes at 1 atm:  (a) ammonia melts at -60 C, (b) ammonia melts at -77.7 C, and (c) ammonia melts at -100 C.  (The normal melting point of ammonia is -77.7 C.)

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Expert Answer

Step 1

(a)Given,

Normal melting point of ammonia is -77.7 degree Celsius.

In this reaction, ammonia melts at -60 degree Celsius.

During melting, there is a change in phase of ammonia from solid to liquid, which leads to increase in number of particles.  Thus, the sign of change in entropy is positive.  Next, change in enthalpy of this reaction is a endothermic reaction, in which heat transfers from surroundings to system(heat absorption).  Therefore, the sign of change in enthalpy is positive.  Also, temperature of ammonia is greater than its normal melting point, so

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Step 2

(b)Given,

Normal melting point of ammonia is -77.7 degree Celsius.

In this reaction, ammonia melts at -77.7 degree Celsius.

During melting, there is a change in phase of ammonia from solid to liquid, which leads to increase in number of particles.  Thus, the sign of change in entropy is positive.  Next, change in enthalpy of this reaction is neither endothermic nor exothermic reaction because there is no change in temperature.  Therefore, the sign of change in enthalpy is neutral (zero).  Hence, the change in Gibbs free energy is given as

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Step 3

(c)Given,

Normal melting point of ammonia is -77.7 degree Celsius.

In this reaction, ammonia melts at -60 degree Celsius.

During this reaction, there is no change in phase of ammonia from solid to liquid.  Thus, the sign of change in entropy is negative.  Next, change in enthalpy of ...

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