Presumptive tests, also known as preliminary tests or field tests, allow drugs to be quickly classified into a particular chemical group, but do not unequivocally identify the presence of a specific chemical compound.
<u>Answer:</u> The correct statement is low temperature only, because entropy decreases during freezing.
<u>Explanation:</u>
The relationship between Gibb's free energy, enthalpy, entropy and temperature is given by the equation:
Where,
= change in Gibb's free energy
= change in enthalpy
T = temperature
= change in entropy
It is given that freezing of methane is taking place, which means that entropy is decreasing and 
is becoming negative. It is also given that the reaction is an exothermic reaction, this means that the is also negative.
For a reaction to be spontaneous, must be negative.
![-ve=-ve-[T(-ve)]\\\\-ve=-ve+T](https://tex.z-dn.net/?f=-ve%3D-ve-%5BT%28-ve%29%5D%5C%5C%5C%5C-ve%3D-ve%2BT)
From above equations, it is visible that will be negative only when the temperature will be low.
Hence, the correct statement is low temperature only, because entropy decreases during freezing.
Answer:
Explanation:
2NO₂ ⇌ N₂O₄
E/mol·L⁻¹: 0.058 0.012
K_{\text{eq}} = \dfrac{\text{[N$_{2}$O$_{4}$]}}{\text{[NO$_{2}$]$^{2}$}} = \dfrac{0.012}{0.058^{2}} = \mathbf{3.6}
\\\\
\text{The $K_{\text{eq}}$ value would be $\boxed{\mathbf{3.6}}$}
A stoichiometric mixture is a mixture of fuel and oxygen for which the masses of these two components are exactly those needed for complete combustion.
A stoichiometric mixture is a balanced mixture of fuel and oxygen.
The fuel and the oxygen react completely without the excesses of either.
The opposite of a stoichiometric mixture is called feeding an excess, when minimum one reactant is an excess amount.
Balanced chemical equation for reaction of combustion one type of a fuel: C₈H₁₈ + 25/2O₂ → 8CO₂ + 9H₂O
Stoichiometric mixture for this example is when fuel (C₈H₁₈) and oxygen(O₂) react in proportion 1 : 12.5.
More about a stoichiometric mixture: brainly.com/question/19585982
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Answer is C. in a reaction mole stays the same but mass changes and since it produced gas it means now we have less mass.
