How do you know that given chemical equation is exothermic or endothermic?

Answer 1

Chemical reactions are about making and breaking bonds. You have to add up how much energy is used to break the chemical bonds of the reactants, and subtract this from the total amount of energy used to make the bonds of the product(s). To do this, you need to know how much energy is needed to make/break each bond. Here are some examples: C-H 98 O-H 110 C-C 80 C-O 78 H-H 103 C-N 65 O=O 116(2 x 58) C=O 187(2 x 93.5) C=C 145 (2 x 72.5) These are all in kcal/mole. When you've worked this out, if the end number is negative then the reaction is exothermic, if the answer's positive, then it's endothermic. Alternatively you could just try the experiment yourself.

Answer 2

You can determine if a chemical reaction is exothermic or endothermic by calculating the change in enthalpy (ΔH) for the reaction. If ΔH is negative, the reaction is exothermic, releasing heat to the surroundings. If ΔH is positive, the reaction is endothermic, absorbing heat from the surroundings.

Answer 3

An exothermic process will give off heat, while an endothermic process will use up heat.

Answer 4

exothermic reaction evolves heat

endothermic reaction absorbs heat