How do you know whether a chemical reaction is exothermic or endothermic?

How to know if a Chemical reaction is a exothermic or a endothermic?

• I do know that an exothermic reaction is what "gives out" energy and the Endothermic which does the opposite but how to know if the chemical reaction that is given to you (regardless of weither it being in Equation forms or not) is an exothermic or an endothermic reaction? There is a part in my question saying "Name these reactions of being a exothermic or endothermic write the answer beside them A.)The condensation of steam of water B.)The burning of magnesium C.)The addition of concentrated Sulfuric acid to water D.)the evaporation of a volatile liquid" You can give equations in your answer for explaining

• Answer:

  A) When a compound undergoes a phase change, such as steam (which is the vapor form of water) to liquid water, there will always be either a consumption of energy or a release of energy. The direction of the energy depends on what direction the phase change is occuring. Another way to think about this is to look at temperature and energy phase diagram. T...|...................________/ E...|...________/ M..|../ P...|/_________________________________… ......................... Energy Each of the straight lines on the chart represent a phase change. For this first question, we are looking at that top line. As water condenses from a higher temperature to a lower temperature, what happens to energy? It decreases. This energy has to go somewhere... so it is released to the atmosphere in an EXOTHERMIC transition. B) Whenever a compound burns, it gives off alot of heat and energy as it reacts with oxygen to combust. This is exothermic. C) This is highly exothermic as the water acts as a weak base which causes a violent acid-base reaction to occur which generates a lot of heat. D) This is the opposite of A. Still using that chart, now we are moving from left to right. A volatile liquid is one whose vapor pressure exceeds that of the atmospheres vapor pressure. In order to keep it as a liquid, we keep it extremely cold. The second we allow it to approach room temperature, it will absorb the energy from the air to evaporate.