Here are the solutions to the questions: 65. When sodium dioxonitrate (III) ($\text{NaNO}_2$) dissolves in water $\Delta H$ is positive, the process of dissolution is A positive value for the enthalpy change ($\Delta H$) indicates that the reaction absorbs heat from its surroundings. This type of reaction is defined as endothermic*. The correct option is (b) endothermic*. 66. The energy change ($\Delta H$) for the reaction $\text{CO}_{(g)} + \frac{1}{2}\text{O}_{2(g)} \rightarrow \text{CO}_{2(g)}$ is We use Hess's Law, which states that the enthalpy change of a reaction