The bond energy of a chemical bond is the energy required to 1 mole of the bond in the phase. Because bonds is endothermic and bonds is exothermic, we can calculate the overall enthalpy change as a of the enthalpy changes associated with the required bonds in the reactants and the required bonds in the products.

The bond energy of a chemical bond is the energy required to 1 mole of the bond in the phase, the amount of energy released equals the difference between the energies of the bonded atoms and the energies of the independent atoms.

Because bonds is endothermic and bonds is exothermic, we can calculate the overall enthalpy change as a of the enthalpy changes associated with the required bonds in the reactants and the required bonds in the products, each molecule has its own characteristic bond energy, but some generalizations are possible

Explanation:

Compounds make atoms attain lower energies compared with what they attain as individual atoms. The amount of energy released in the bonded atoms is heat so the compound has a lower overall energy, it is called enthalpy change and it is positive, these are exothermic reactions, where the energy released, is a product

Within a chemical reaction, breakage, caused by energy, on molecular bonds cause other bonds to be formed into different molecules, so the enthalpy change is negative because the system is releasing energy as the bond is formed these are endothermic reactions, where the energy required is a reactant.

pre-sliced bread is a relatively recent development in baking technology. previous to that, it was always sold in a bakery in daily-made contiguous loaves with no wrapping, and was moderately perishable, usually being used with a day or two (which is why every bakery had a discounted “day-old” bread table.) therefore, pre-sliced bread would grow stale quickly. the hard crust provided a protective layer, and once the exposed dry slice left from the previous cut was removed, the interior was still soft.

what keeps bread soft is the moisture retained in the crumb (the light spongy part that’s not crust). the reason the crust develops is the surface of the dough gets exposed to hot dry air during baking which browns the outer layer and seals it, preventing all the moisture from escaping the dough. longer exposure to air will also eventually cause your bread to lose flavor and become stale.

people were used to cutting slices as they needed them and storing bread in a specially-made wooden or metal breadbox or pail with a lid to preserve it longer, but the first automatically sliced commercial loaves were produced on july 6, 1928, in chillicothe, missouri, using a machine invented by otto rohwedder, an iowa-born, missouri-based jeweler.[1] pre-sliced bread would indeed dry out, were it not for another 20th century technology: the plastic bag. bread could now be pre-sliced, and if the enclosing bag remains sealed as much as possible, the bread will remain soft and fresh for longer than if sitting unwrapped on a shelf or enclosed in a bread box that is not air-tight. sealed packaging meant bread could also be sold on store shelves and eliminate frequent trips to a bakery.

sealing bread in a plastic bag had another effect: the moisture in the loaf will re-distribute into the crust and soften it, which is sometimes more pleasing in a sandwich - especially for children whose teeth might not yet be strong enough to tear through a hard crust. a homemade loaf of bread can be sealed in a bag overnight and the crust will become soft like store-bought sandwich bread.

these were novel changes in how bread was produced and sold, which led to the coining of the phrase “the greatest thing since sliced bread.”