An electric device delivers a current of [tex]$15.0 A$[/tex] for 30 seconds. How many electrons flow through it?
Answer (1)
Analyze each reaction to determine the oxidation states of the elements involved.
Identify changes in oxidation states to determine if a reaction is a redox reaction.
Reaction 3, C ( s ) + O 2 ( g ) → C O 2 ( g ) , shows carbon changing from 0 to +4 and oxygen changing from 0 to -2.
Therefore, the redox reaction is: C ( s ) + O 2 ( g ) → C O 2 ( g ) . C ( s ) + O 2 ( g ) → C O 2 ( g )
Explanation
Identifying Redox Reactions We need to identify the redox reaction from the given list of reactions. A redox reaction involves a change in oxidation state for at least two elements. Let's analyze each reaction.
Analyzing Reaction 1 Reaction 1: 2 A lC l 3 ( a q ) + 3 N a 2 S ( a q ) → 6 N a Cl ( a q ) + A l 2 S 3 ( s ) .
Aluminum (Al) goes from +3 in A lC l 3 to +3 in A l 2 S 3 . No change.
Chlorine (Cl) goes from -1 in A lC l 3 to -1 in N a Cl . No change.
Sodium (Na) goes from +1 in N a 2 S to +1 in N a Cl . No change.
Sulfur (S) goes from -2 in N a 2 S to -2 in A l 2 S 3 . No change. Since there are no changes in oxidation states, this is not a redox reaction.
Analyzing Reaction 2 Reaction 2: 2 ( N H 4 ) 3 P O 4 ( a q ) + 3 C a ( N O 3 ) 2 ( a q ) → C a 3 ( P O 4 ) 2 ( s ) + 6 N H 4 N O 3 ( a q ) .
Calcium (Ca) goes from +2 in C a ( N O 3 ) 2 to +2 in C a 3 ( P O 4 ) 2 . No change.
Nitrogen (N) goes from -3 in ( N H 4 ) 3 P O 4 to -3 in N H 4 N O 3 and +5 in C a ( N O 3 ) 2 to +5 in N H 4 N O 3 . No change.
Phosphorus (P) goes from +5 in ( N H 4 ) 3 P O 4 to +5 in C a 3 ( P O 4 ) 2 . No change.
Oxygen (O) goes from -2. No change.
Hydrogen (H) goes from +1. No change. Since there are no changes in oxidation states, this is not a redox reaction.
Analyzing Reaction 3 Reaction 3: C ( s ) + O 2 ( g ) → C O 2 ( g ) .
Carbon (C) goes from 0 in C to +4 in C O 2 . Oxidation state changes.
Oxygen (O) goes from 0 in O 2 to -2 in C O 2 . Oxidation state changes. Since the oxidation states of both carbon and oxygen change, this is a redox reaction.
Analyzing Reaction 4 Reaction 4: H Cl ( a q ) + N H 4 O H ( a q ) → N H 4 Cl ( a q ) + H 2 O ( l ) .
Hydrogen (H) goes from +1. No change.
Chlorine (Cl) goes from -1 in H Cl to -1 in N H 4 Cl . No change.
Nitrogen (N) goes from -3 in N H 4 O H to -3 in N H 4 Cl . No change.
Oxygen (O) goes from -2 in N H 4 O H to -2 in H 2 O . No change. Since there are no changes in oxidation states, this is not a redox reaction.
Conclusion Only reaction 3, C ( s ) + O 2 ( g ) → C O 2 ( g ) , is a redox reaction because the oxidation states of carbon and oxygen change during the reaction.
Examples
Redox reactions are essential in many areas, including energy production (combustion of fuels), corrosion (rusting of iron), and biological processes (cellular respiration). For example, the burning of wood is a redox reaction where carbon in the wood combines with oxygen in the air to produce carbon dioxide and water, releasing heat and light. Understanding redox reactions helps us to control and utilize these processes effectively.
