VITEEE 2019 :: Chemistry :: General questions

• Chemistry - General questions

In a hydrogen-oxygen fuel cell, combustion of hydrogen occurs to :

Answer:

Explanation:

In a hydrogen-oxygen fuel cell, following reactions take place to create a potential difference between the two electrodes.

$2H_{2} (g) + 4OH^{-}(aq) \rightarrow 4H2O (l) + 4e^{-}$

$O_{2} (g) + 2H_{2}O(l) + 4e^{-} \rightarrow 4OH^{-}(aq)$

$Overall reaction = 2H_{2} (g) + O_{2} (g) \rightarrow 2H_{2}O(l)$

the net reaction is the same as burning (combustion) of hydrogen to form water.

Phosphine is generally prepared in the laboratory:

Answer:

Explanation:

$P_{4}+3NaOH+3H_{2}O\rightarrow PH_{3}+3NaH_{2}PO_{2}$

White                                                   Phosphine

The uncertainty in position and velocity, of a particle, are 10^-10m and 5.27 x 10^-24 ms^-1 respectively. Calculate the mass of the particle is (h =[ 6.625 x 10^-34 Js) 

Answer:

Explanation:

According to Heisenberg's uncertainty principle,

$Δx.mΔv = \frac{h}{4\pi}$

or $m= \frac{h}{4\piΔx.Δv}$ = 

$\frac{6.625\times 10^{-34}Js}{4\times3.143\times 10^{-10}m\times5.27\times 10^{-24}m/s}$

= 0.099 kg (J =kgm²s²)

Calculate the energy needed to convert three moles of sodium atoms in the gaseous state to sodium ions. The ionization energy of sodium is 495 kJ/mol

Answer:

Explanation:

Energy needed to convert 1 mole of sodium (g) to sodium ions = 495 kJ

.'. Energy needed to convert 3 moles of Na(g) to Na⁺ ions

= 495 x 3 =  1485 kJ

The rate constant is doubled when the temperature increases from 27°C to 37°C. Activation energy in kJ is

Answer:

Explanation:

$log\frac{K_{2}}{K_{1}}$= $\frac{E_{a}}{2.303R}\left[\frac{1}{T_{1}}- \frac{1}{T_{2}}\right]$

If $log\frac{K_{2}}{K_{1}}$ = 2

log 2 = $\frac{E_{a}}{2.303\times8.314}\left[\frac{1}{300}- \frac{1}{310}\right]$

$E_{a} = 0.3010\times2.303\times8.314\left(\frac{300\times310}{10}\right)$

= 53598.59 J/mol = 54kJ

• Chemistry - General questions