When hydrogen reacts with chlorine the gas hydrogen chloride is produced: H2(g) + Cl2(g) → 2HCl(g) Calculate the energy change of the reaction and state whether the reaction is exothermic or endothermic.

How does a hydroelectric power plant converts energy into energy.

An atom of sodium-23 (atomic number = 11) has a positive charge of +1. give this information, how many electrons does it have? how many proteins and neutrons does this atom have

An electron moved from shell n = 2 to shell n = 1. what most likely happened during the transition? a fraction of a photon was added. a photon of energy was absorbed. a fraction of a photon was removed. a photon of energy was released.