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Thermochemical Equation - Concept

Teacher/Instructor Kendal Orenstein
Kendal Orenstein

Rutger's University
M.Ed., Columbia Teachers College

Kendal founded an academic coaching company in Washington D.C. and teaches in local area schools. In her spare time she loves to explore new places.

Thermochemical equations are balanced chemical equations that include the physical states of all reactants and products and the energy change. If energy is a reactant, the reaction is endothermic but if energy is a product, the reaction is exothermic.

Alright so sometimes when you're dealing with balanced thermo chemical equations you're going to want to include the amount of energy that's either being absorbed or released in that reaction. So we're going to call those guys thermo chemical equations and they're balanced chemical equations that include the physical states of all reactants and products which they should always have and the energy change. We're going to call this delta H or enthalpy change. Okay so I have on the board several different types of reactions that, and I have also included their enthalpy changes or energy changes in it. So we have our first reaction which is just a simple combination reaction or a synthesis reaction. And notice that the delta H is 1625 kilo joules meaning that it's releasing that much energy into the atmosphere. So when these 2 guys combine and form rust, we're releasing 1625 kilo joules of heat okay great.

We also have a reaction or this is actually a solubility reaction. What we have is substance ammonium nitrate it's being dissolved in some water and breaking up to it's ions and it's actually going to require some energy 27 kilo joules of energy you've noticed that there's no negative here telling me that I'm requiring that much energy to make this reaction take place it's an endothermic reaction okay great. Then we also have combustion reactions all have been, we're going to actually denote that as delta H comb to say that this is a combustion reaction. Okay so we have our glucose combusting and we're saying it's releasing 2,808 kilo joules of heat, it's a lot of energy when reaction occur. And we're going to just, that little comb is just telling me this is delta H of a combustion reaction.

Down here we have phase changes, phase changes can also go through energy changes that require energy or release some sort of energy. This is water going from liquid to a gas, just a simple phase change and it's a vaporization phase change going from liquid to gas vaporizing. So we're going to denote that as delta H vap telling you that this is the vaporization enthalpy and it requires 40.7 kilo joules of heat and then also we can talk about, specify formation reactions meaning that a compound or substance being formed from its elements. So you have hydrogen gas combining with sulfur to form hydrogen sulfide and we're going to say delta H at that form is telling me that this is a formation reaction and it requires 33 kilo joules heat into endothermic. So we can get, just from looking at this basic equation of thermo chemical equation we can get a lot of information from this and these are basically all the different [IB] chemical equations tat you're going to come across.