CBSE Class 10 Answered

• If there is a delta Δ sign in the product side then the heat is evolved during the reaction and if the delta Δ sign is in the reactant side then the heat is absorbed during the reaction.

(Further, (In higher grades) You will be studying in 11th grade)

• If the reactants have weak bonds, while the products have strong bonds then the reaction is exothermic (enthalpy change < 0). There is a small amount of energy needed to break the bond and a bigger energy released when strong bonds form. A negative enthalpy change means that the system releases heat energy.
• If the reactants have strong bonds, but the products have weak bonds its an endothermic reaction. (enthalpy change > 0). The energy required to break the reactant bonds is greater than the energy released when the product bonds form. A positive enthalpy change means that the system absorbs heat energy.