Question

Which of the following processes are endothermic?

A) 2 Br(g) - Br2(g)
B) K*(g) + I(g) → KI(s)
C) Ca(s) - Ca(g)
D) 2 Na(s) + O2(g) → Na2O(s)
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E) None of the above are endothermic.

Answer 1

Among the choices provided, the endothermic process is the sublimation of calcium (Ca(s) to Ca(g)), as it requires the absorption of energy to convert from solid to gas. The correct option is option (C).

Step-by-step explanation:

To determine which of the listed processes are endothermic, we need to understand the concept of endothermic and exothermic reactions. Endothermic reactions absorb energy, typically in the form of heat, from their surroundings, while exothermic reactions release energy.

• 2 Br(g) - Br2(g): The bonding of two bromine atoms into a molecule is typically an exothermic process as bonds are being formed.
• K*(g) + I(g) → KI(s): This represents the formation of an ionic compound, which is an exothermic process due to the release of energy when ionic bonds are formed.
• Ca(s) - Ca(g): Converting calcium from solid to gas involves breaking metallic bonds and is an endothermic process as it requires the intake of energy.
• 2 Na(s) + O2(g) → Na2O(s): The formation of an oxide from sodium and oxygen is an exothermic process because energy is released when chemical bonds are formed.

Therefore, the process that is endothermic among the choices given is C) Ca(s) - Ca(g), which involves the sublimation of calcium and requires the absorption of energy.