WAEC 2024 CHEMISTRY

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(1a)
An electrochemical cell is a device that converts chemical energy into electrical energy or vice versa. It consists of two half-cells, each containing a electrodes (an anode and a cathode) immersed in an electrolyte, which facilitates the flow of ions between the electrodes.

(1b)
(i)Spontaneity: Electrochemical cells are spontaneous, meaning they generate electricity on their own, while electrolytic cells require an external power source to drive the reaction.
(ii)Direction of Electron Flow: In electrochemical cells, electrons flow from the anode to the cathode, while in electrolytic cells, electrons flow from the cathode to the anode.
(iii)Purpose: Electrochemical cells are used to generate electricity, while electrolytic cells are used to drive non-spontaneous reactions, such as electroplating or water splittings.

(1c)
(i)The blue color of the copper sulfate solution starts to fade as zinc replaces the copper.
(ii)Solid copper begins to precipitate out of the solution, forming a reddish-brown deposit at the bottom of the beaker.
(iii)The solution might gradually become colorless if all the copper ions are replaced.
(iv)Bubbles of hydrogen gas may be observed if the zinc is in excess, indicating the occurrence of further reactions involving the zinc and the sulfate or the acidic solution.

(1di)
CH4(g) -> C(s) + 2H2(g)

(1dii)
Decomposition reaction

(1e)
(i) hydrogen chloride (HCl)
(ii)sulfur dioxide (SO2).

(1f)
(i)high temperature
(ii)presence of a catalyst
(iii)longer hydrocarbon chain length.

(1g)
Noble gases are chemically inert because they have a completely filled outer shell of electrons, making them very stable and unlikely to react with other elements.

(1h)
(i)Members have the same general formula
(ii)Members have similar chemical properties
(iii)Members have a gradual change in physical properties
(iv)Members have a constant difference in molecular formula between successive members

(1i)
Global warming refers to the long-term rise in the average surface temperature of the Earth due to the increasing levels of greenhouse gases in the atmosphere.

(j)
increasing levels of carbon dioxide (CO2) in the atmosphere, primarily due to fossil fuel burning, deforestation, and land-use changes.

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