Parmi les réactions suivantes, lesquelles sont des réactions...

Parmi les réactions suivantes, lesquelles sont des réactions d'oxydoréduction? a) $2 \mathrm{CO}+\mathrm{O}_2 \longrightarrow 2 \mathrm{CO}_2$ b) $\mathrm{H}_2+\mathrm{Br}_2 \longrightarrow 2 \mathrm{HBr}$ c) $2 \mathrm{~N}_2 \mathrm{O}_5 \longrightarrow 2 \mathrm{~N}_2 \mathrm{O}_4+\mathrm{O}_2$ d) $2 \mathrm{~K}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow 2 \mathrm{KOH}+\mathrm{H}_2$ e) $\mathrm{NH}_4 \mathrm{NO}_2 \longrightarrow \mathrm{NH}_4^{+}+\mathrm{NO}_2^{-}$ f) $\mathrm{P}_4 \mathrm{O}_{10}+6 \mathrm{H}_2 \mathrm{O} \longrightarrow 4 \mathrm{H}_3 \mathrm{PO}_4$ g) $2 \mathrm{Al}+3 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3+3 \mathrm{H}_2$ h) $\mathrm{S}_8+8 \mathrm{O}_2 \longrightarrow 8 \mathrm{SO}_2$ i) $2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Na}_2 \mathrm{SO}_4+2 \mathrm{H}_2 \mathrm{O}$

Parmi les réactions suivantes, lesquelles sont des réactions d'oxydoréduction?
a) $2 \mathrm{CO}+\mathrm{O}_2 \longrightarrow 2 \mathrm{CO}_2$
b) $\mathrm{H}_2+\mathrm{Br}_2 \longrightarrow 2 \mathrm{HBr}$
c) $2 \mathrm{~N}_2 \mathrm{O}_5 \longrightarrow 2 \mathrm{~N}_2 \mathrm{O}_4+\mathrm{O}_2$
d) $2 \mathrm{~K}+2 \mathrm{H}_2 \mathrm{O} \longrightarrow 2 \mathrm{KOH}+\mathrm{H}_2$
e) $\mathrm{NH}_4 \mathrm{NO}_2 \longrightarrow \mathrm{NH}_4^{+}+\mathrm{NO}_2^{-}$
f) $\mathrm{P}_4 \mathrm{O}_{10}+6 \mathrm{H}_2 \mathrm{O} \longrightarrow 4 \mathrm{H}_3 \mathrm{PO}_4$
g) $2 \mathrm{Al}+3 \mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Al}_2\left(\mathrm{SO}_4\right)_3+3 \mathrm{H}_2$
h) $\mathrm{S}_8+8 \mathrm{O}_2 \longrightarrow 8 \mathrm{SO}_2$
i) $2 \mathrm{NaOH}+\mathrm{H}_2 \mathrm{SO}_4 \longrightarrow \mathrm{Na}_2 \mathrm{SO}_4+2 \mathrm{H}_2 \mathrm{O}$

Key Concepts

Redox Reaction

A redox reaction is a chemical process in which electrons are transferred between reactants, resulting in changes in their oxidation states. This concept is central in chemistry because it describes how substances undergo oxidation (loss of electrons) and reduction (gain of electrons) simultaneously.

Oxidation

Oxidation refers to the process where a chemical species loses electrons, leading to an increase in its oxidation number. Recognizing the substance that is oxidized is crucial to understanding the overall electron flow in redox reactions.

Reduction

Reduction is the process in which a chemical species gains electrons, thereby experiencing a decrease in its oxidation number. This concept is typically discussed alongside oxidation as both processes occur together in a redox reaction.

Oxidation State

The oxidation state is an indicator of the degree of oxidation of an atom in a compound. Changes in oxidation states during a reaction help identify the substances undergoing oxidation and reduction, thereby confirming if a reaction is a redox process.

Electron Transfer

Electron transfer is the fundamental process behind redox reactions. It involves the movement of electrons from the oxidized species to the reduced species, and understanding this transfer is key to analyzing and balancing redox reactions.

Transcript

00:01 There are several reactions listed in this problem, and we need to identify whether or not they are redox reactions.

00:07 To do that, it's best to identify the oxidation numbers first, and then see if there's a change yet the oxidation number.

00:15 We see sodium going from an oxidation state of zero and chlorine, an oxidation state of zero, to sodium now 1 plus and chlorine now chloride.

00:25 Because there is a change in the oxidation number, then this is definitely a redox reaction.

00:31 We then go to the second reaction where carbon reacts with oxygen forming carbon dioxide, and we assign oxidation numbers, zero on carbon, zero on oxygen.

00:41 We then go to carbon dioxide and the oxidation number of carbon has become plus four and oxygen minus two.

00:50 So also a change in oxidation number, therefore this is a redox reaction.

00:55 Reaction three, we have two waters reacting with each other, forming two hydrogens and two oxygens.

01:03 Using the oxidation number rules, oxygen is minus two, hydrogen is plus one.

01:08 Then when we go to their elemental forms, each of them are zero.

01:12 So this is also a change in oxidation number, definitely a redox reaction.

01:18 Then for the fourth one, we have sodium chloride reacting with silver nitrate.

01:23 And if we look closely, we simply see that there is a switching of partners, the cat ions switch places.

01:34 And as the cat ions switch places, there is no change in charge or oxidation number.

01:39 Because of this, this is a simple precipitation reaction, recognizing that this ends up becoming a solid of sodium chloride, so not a redox reaction.

01:50 Then the next one, we have ammonia reacting with hcl, producing nh4 plus ammonium and the chloride anion.

02:01 Here we just have an exchange of a hydrogen...

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