Nitrogen is 78.08% of the air is fills the earth's atmosphere.
The Reaction is spontaneous when temperature is 430 K. Hence, Option (C) is correct.
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What is Spontaneous reaction ?</h3>
Reactions are favorable when they result in a decrease in enthalpy and an increase in entropy of the system.
When both of these conditions are met, the reaction occurs naturally.
Spontaneous reaction is a reaction that favors the formation of products at the conditions under which the reaction is occurring.
According to Gibb's equation:
ΔG = ΔH - TΔS
ΔG = Gibbs free energy
ΔH = enthalpy change = +62.4 kJ/mol
ΔS = entropy change = +0.145 kJ/molK
T = temperature in Kelvin
- ΔG = +ve, reaction is non spontaneous
- ΔG = -ve, reaction is spontaneous
- ΔG = 0, reaction is in equilibrium
ΔH - TΔS = 0 for reaction to be spontaneous
T = ΔH / ΔS
Here,
T = 500K
Thus the Reaction is spontaneous when temperature is 500 K.
Learn more about Gibbs free energy here ;
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Answer:
2.25g of NaF are needed to prepare the buffer of pH = 3.2
Explanation:
The mixture of a weak acid (HF) with its conjugate base (NaF), produce a buffer. To find the pH of a buffer we must use H-H equation:
pH = pKa + log [A-] / [HA]
<em>Where pH is the pH of the buffer that you want = 3.2, pKa is the pKa of HF = 3.17, and [] could be taken as the moles of A-, the conjugate base (NaF) and the weak acid, HA, (HF). </em>
The moles of HF are:
500mL = 0.500L * (0.100mol/L) = 0.0500 moles HF
Replacing:
3.2 = 3.17 + log [A-] / [0.0500moles]
0.03 = log [A-] / [0.0500moles]
1.017152 = [A-] / [0.0500moles]
[A-] = 0.0500mol * 1.017152
[A-] = 0.0536 moles NaF
The mass could be obtained using the molar mass of NaF (41.99g/mol):
0.0536 moles NaF * (41.99g/mol) =
<h3>2.25g of NaF are needed to prepare the buffer of pH = 3.2</h3>
The best option is melting point