Which of the following represents the first law of thermodynamics?
U = q + W
U = p . V
H = q + W
When solid melts, there will be
a decrease in enthalphy
a decrease in free energy
a decrease in entropy
all the above factors remain constant
B.
a decrease in free energy
When a solid substance changes into its liquid state at its melting point, the process takes place by absorption of heat from the surroundings. e.g., melting of ice
H2O (s) H2O (l)
Thus, enthalpy change for this process is positive or there is an increase in enthalpy, but still the reaction is spontaneous, because the liquid state ofwateris more random than its solid state. Hence, it may be concluded that melting of ice is accompanied by an increase of entropy.
For a reaction to be spontaneous, the value of G, i.e., the Gibbs' free energy change must be negative or there must be a decrease in free energy, thus, H must be smaller than TS.
To convert 94 g of ice at 0°C into 94g of vapour at 100° C, the quantity of coal (90% carbon) required is : (ΔHc of carbon = -94 k cal mol-1);latent heat of fusion = + 80 cal per gm; latent heat ofvaporisation=+ 540 cal per gm; specificheat of water = 1 cal per gm per °C).
94g
80g
9.4g
9.6 g
When 1 M H2SO4 is completely neutralized by NaOH, the heat liberated is 114.64 kJ. What is the enthalpy of neutralization?
+ 114.64 kJ
-114.64 kJ
-57.32 kJ
+ 57.32 kJ
What is the free energy change G when 10 moles of water at 100°C and 1 atm pressure is converted into steam at 100° C and 1 atm pressure?
540 cal
-9800 cal
9800 cal
0 cal
In which of the following ?
N2O4 (g) 2NO2 (g)
2SO2 (g) + O2 (g) 2SO3 (g)
H2 (g) + I2 (g) 2HI (g)
H2 (g) + O2 (g) H2O (l)
Match List I with List II and select the correct answer using the codes.
List I | List II |
A. Spontaneous process | 1 Δh < 0 |
B. Exothermic process | 2. Heat of reaction |
C. Enthalpy at constant pressure | 3. ΔG < 0 |
D. Cyclic process | 4. ΔU= 0, ΔH = 0 |
A B C D
4 2 1 3
A B C D
3 1 2 4
A B C D
1 3 4 2
A B C D
1 2 3 4