Physics, 27.11.2019 23:31 NetherisIsTheQueen

Explain why the following reaction occurs:
zn + 2hcl → zncl2 + h,

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The reaction $\rm Zn\, (s) + 2\, HCl \, (aq) \to ZnCl_2\, (aq) + H_2\, (g)$ is spontaneous (under standard conditions) because the cell potential is positive.

Explanation:

In this reaction:

Metallic zinc $\rm Zn\, (s)$ is oxidized to produce zinc ions $\rm Zn^{2+}$ . Hydrogen ions $\rm H^{+}$ is reduced to produce hydrogen gas $\rm H_2\, (g)$ .

The anode is where the oxidation half-reaction takes place. In this case, the anode half-reaction is $\rm Zn\, (s) \to Zn^{2+} \, (aq) + 2\, e^{-}$ .

The cathode is where the reduction half-reaction takes place. In this case, the cathode half-reaction is $\rm 2\, H^{+}\, (aq) + 2\, e^{-} \to H_2\, (g)$ .

Look up the standard reduction potential for these two half-reactions:

$E^{\circ}_{\text{reduction, anode}} = \rm -0.7618\; V$ for the reaction $\rm Zn^{2+} \, (aq) + 2\, e^{-} \rightleftharpoons Zn\, (s)$ . $E^{\circ}_{\text{reduction, cathode}} = \rm 0\; V$ for the reaction $\rm H^{+} \, (aq) + e^{-} \rightleftharpoons \dfrac{1}{2}H_2\, (g)$ .

The standard cell potential is equal to the standard reduction potential at the cathode minus that at the anode:

$E^{\circ}_\text{cell} = E^{\circ}_{\text{reduction, cathode}} - E^{\circ}_{\text{reduction, anode}} = \rm 0.7618\; V$ .

The electrochemical reaction in the cell is spontaneous if and only if the cell potential is positive. Therefore, the reaction $\rm Zn\, (s) + 2\, HCl \, (aq) \to ZnCl_2\, (aq) + H_2\, (g)$ is spontaneous under standard conditions.

Answer from: Quest

radiation warms things up temp rises convection currents air circ windy weather

Answer from: Quest

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.

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Explain why the following reaction occurs:
zn + 2hcl → zncl2 + h,...

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