Jorja De Jesus 2C
Posts: 121
Joined: Sat Jul 20, 2019 12:15 am

How do you know whether heat is added or released just by looking at the equation?

Maggie Eberhardt - 2H
Posts: 97
Joined: Sat Jul 20, 2019 12:16 am

I would also like to know

MinuChoi
Posts: 100
Joined: Wed Sep 18, 2019 12:15 am

I think you could find this by determining of the reaction is exothermic or endothermic reactions (endothermic reactions require a heat input). Sometimes you can tell this just by looking at the reaction. Ex. If the rxn is one reactant being broken into several products, it's probably exothermic because energy would be required to break the bonds of the larger reactant molecule.

Juliana Chopelas 1A
Posts: 50
Joined: Sat Aug 24, 2019 12:16 am

It is not necessarily obvious without looking in tables for energies and enthalpies. You can try to guess by looking to see if bonds are broken and formed but you won't truly know until you calculate to see if a reaction is exothermic or endothermic.

005206171
Posts: 107
Joined: Wed Sep 18, 2019 12:20 am

Forming new bonds releases energy. In a synthesis reaction where you’re forming a new product from its reactants, energy will be released because the new product is more stable. Breaking bonds requires energy. In decomposition reactions where you’re breaking apart a molecule into its simpler parts, you will need energy = endothermic. Also look at enthalpy, the sign will tell you if energy is being released (negative) or require (positive). Heat can also be directly
In the products or reactants side of the equation.

Alondra
Posts: 36
Joined: Tue Feb 26, 2019 12:15 am

If there is no delta H + or - stated in the problem then look at the products and reactants in the rxn and consider bonds being formed or broken.

Nathan Rothschild_2D
Posts: 131
Joined: Fri Aug 02, 2019 12:15 am