Question

reactions with a positive change in enthalpy --

are exothermic because the positive change in enthalpy means heat is released by the system

are exothermic because the positive change in enthalpy means heat is absorbed by the system

are endothermic because the positive change in enthalpy means heat is released by the system

are endothermic because the positive change in enthalpy means heat is absorbed by the system

Explanation:

To determine the correct option, we recall the definitions of enthalpy change (\(\Delta H\)) for endothermic and exothermic reactions:

• In an endothermic reaction, the system absorbs heat from the surroundings. This is associated with a positive \(\Delta H\) (since the system's enthalpy increases, \(\Delta H = H_{products}-H_{reactants}>0\) when \(H_{products}>H_{reactants}\)).
• In an exothermic reaction, the system releases heat to the surroundings. This is associated with a negative \(\Delta H\) (since \(H_{products}

Now let's analyze each option:

1. First option: Claims positive \(\Delta H\) means exothermic (heat released). But exothermic has \(\Delta H < 0\), so this is incorrect.
2. Second option: Claims positive \(\Delta H\) means exothermic (heat absorbed). Exothermic releases heat, and positive \(\Delta H\) is not exothermic, so this is incorrect.
3. Third option: Claims positive \(\Delta H\) means endothermic but says heat is released. Endothermic absorbs heat, so this is incorrect.
4. Fourth option: Claims positive \(\Delta H\) means endothermic (heat absorbed). This matches the definition of endothermic reactions (positive \(\Delta H\) as system gains enthalpy by absorbing heat).

Answer:

The correct option is: "are endothermic because the positive change in enthalpy means heat is absorbed by the system" (the fourth option among the given choices).