Question

what statement best describes reaction 4?

1. hcl + naoh → h₂o + nacl + 57 kj
2. mg(oh)₂ + 37 kj → mgo + h₂o

the energy is destroyed.
the energy is negative.
the energy is positive.
the energy is released.

Explanation:

• According to the law of conservation of energy, energy cannot be destroyed, so the option "The energy is destroyed" is wrong.
• In reaction 4, energy is on the reactant side (input energy), which means it is an endothermic reaction. For endothermic reactions, the energy change ($\Delta H$) is positive. In reaction 3 (an exothermic reaction, energy on the product side), the energy change ($\Delta H$) is negative.
• Since energy is on the reactant side (absorbed), it is not released. So "The energy is released" is wrong.

Answer:

The energy is positive.