What is an endothermic reaction

Astudent carefully transfers 30 g of water and 30 g of alcohol in a glass tube, forming two layers and filling the tube completely. after sealing the tube, the student mixes the solutions, and notices a bubble that forms in the tube. what is the mass of the contents in the glass tube after mixing?

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Element before carbon on the periodic table