Sure, let's delve into the detailed explanation of each process and indicate whether the enthalpy change (∆H) is positive or negative, and classify the process as endothermic or exothermic.
(i) An ice cube melts.
When an ice cube melts, the solid water (ice) absorbs heat from its surroundings to change its phase from solid to liquid. This process requires energy because you need to break the hydrogen bonds holding the ice's crystal structure together.
Step-by-step analysis:
1. Initial state: Ice (solid water) at 0°C.
2. Final state: Liquid water at 0°C.
3. Energy change: To melt, ice absorbs heat from its surroundings.
Since heat is absorbed from the surroundings, the enthalpy change (∆H) is positive.
Conclusion:
- Sign of ∆H: Positive
- Process: Endothermic (since it absorbs heat)
(ii) Combustion of 1 g of butane (C4H10) in sufficient oxygen to give complete combustion to CO2 and H2O.
Combustion is a chemical reaction where a fuel reacts with oxygen to produce heat and typically produces carbon dioxide (CO2) and water (H2O) as byproducts. The combustion of butane is represented by:
[tex]\[ 2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O \][/tex]
In this case, butane is the fuel that releases energy when it combusts with oxygen.
Step-by-step analysis:
1. Initial state: Butane (C4H10) and oxygen (O2).
2. Final state: Carbon dioxide (CO2) and water (H2O).
3. Energy change: Combustion releases a significant amount of energy as heat.
Since heat is released to the surroundings, the enthalpy change (∆H) is negative.
Conclusion:
- Sign of ∆H: Negative
- Process: Exothermic (since it releases heat)
To summarize:
1. Melting of an ice cube is an endothermic process with a positive ∆H.
2. Combustion of butane is an exothermic process with a negative ∆H.
