Question

How to know the enthalpy of reaction whether it is positive or negative without calculations?

Answer 1

During any chemical reaction, heat can be either taken in from the environment or released out into it. The heat exchange between a chemical reaction and its environment is known as the enthalpy of reaction, or H. However, H can't be measured directly - instead, scientists use the change in the temperature of a reaction over time to find the change in enthalpy over time (denoted as $\Delta H)$. With $\Delta H$, a scientist can determine whether a reaction gives off heat (or "is exothermic") or takes in heat (or "is endothermic"). In general, $\Delta H=m\times s\times \Delta T$, where m is the mass of the reactants, s is the specific heat of the product, and $\Delta T$ is the change in temperature from the reaction.