Question

How do primary batteries differ from secondary batteries?

Answer 1

Primary batteries are not rechargeable, meaning that once the chemical reaction has taken place, the battery cannot be reused. An example is the common alkaline battery, where the zinc undergoes oxidation and the manganese dioxide undergoes reduction, and once the reactants are exhausted, the battery is dead. On the other hand, secondary batteries are rechargeable. For example, a lead-acid battery is a secondary battery where the reaction is reversible, allowing the battery to be recharged by reversing the flow of current.

Answer 2

The constant potential of the Mercury cell is due to the fact that the overall reaction does not involve any ion in solution whose concentration can change during the cell's life. The reaction is: \[ \text{HgO (s)} + \text{Zn (s)} \rightarrow \text{Hg (l)} + \text{ZnO (s)} \] Since the concentration of solid zinc and mercury oxide remains constant throughout the process, the cell's potential remains stable at 1.35 V throughout the life of the battery.

Answer 3

The lead storage battery undergoes the following reactions during discharging and recharging: During discharging: \[ \text{PbO}_2 (s) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{PbSO}_4 (s) + \text{H}_2\text{O} (l) \] During recharging, the following reactions occur: Cathode reaction: \[ \text{PbSO}_4 (s) + 2e^- \rightarrow \text{Pb}(s) + \text{SO}_4^{2-} (aq) \] Anode reaction: \[ \text{PbSO}_4 (s) + 2\text{H}_2\text{O} (l) \rightarrow \text{PbO}_2 (s) + \text{SO}_4^{2-} (aq) + 4\text{H}^+ (aq) + 2e^- \] OR:
The overall reaction during recharging is: \[ \text{PbSO}_4 (s) + 2\text{H}_2\text{O} (l) \rightarrow \text{PbO}_2 (s) + \text{Pb}(s) + \text{SO}_4^{2-} (aq) + 4\text{H}^+ (aq) \] Additional advantages of fuel cells over other galvanic cells:
(i) Fuel cells are more efficient because they convert chemical energy directly into electrical energy without the need for mechanical processes, making them more efficient compared to thermal power generation.
(ii) Fuel cells are pollution-free because they produce only water and heat as byproducts, unlike other batteries or power sources that release harmful gases such as CO2