Chemical Reactions

Chemical Reactions is an ultimate tool for balancing chemical reactions, manipulation with chemical equations, investigation of complex reaction mechanisms and combining of the multistep process thermodynamic parameters, such as enthalpy (heat release/absorption) and equilibrium constants.

The application interface consists of four reaction rows; each one of which is provided with the following functional elements:

Multiplier: Sets integer value, defining how many times this reaction proceeds during the process. Simultaneously recalculates values of stoichiometric coefficients, enthalpy and equilibrium constant. Should be changed only after balanced reaction is set. To reset multiplier, delete all digits in the field and press done button in the keyboard! Application automatically recalculates all values after pressing done button in the keyboard!

Balance button (=): Balances the provided reaction. Ignores the already provided coefficients. Application automatically present final reaction after pressing done button in the keyboard! Does not intended to work with redox, radical and electron flow reactions, instead consider Electrochemistry app!

Reaction: The field to type in reactants and products divided by =. Charge or unpaired electrons (in free radicals), if exist must be provided as well, separated by coma: Na,+ ; R,: . Application automatically presents final reaction after pressing done button in the keyboard! Swipe the field from left-to-right to reverse the reaction, by swapping reactants and products. Enthalpy and equilibrium constant are adjusted on the fly. Useful for investigation of complex reaction mechanism. Application automatically present final reaction after pressing done button in the keyboard!

Keq: Equilibrium constant for particular row. Automatically recalculated after change of multiplier. Application automatically recalculates final values after pressing done button in the keyboard!

Enthalpy: Should be negative for exothermic reaction (heat release) and positive for endothermic reaction (heat absorption). Automatically recalculated after change of multiplier.
Application automatically recalculates final values after pressing done button in the keyboard!

Important points

Application supports state indexes: (g), (s), (l), (aq) – all are lowercase only, placed at the end of compound formula. Considered to be a crucial part of a molecule, so same molecules of different states appearing on the opposite sides of equation are not cancelled!

Charges of molecules or unpaired electrons must be placed at the end of molecule and separated by coma. They are also considered to be a crucial part of a molecule, so same molecules that have different charges, appearing on the opposite sides of equation are not cancelled!

Example (presented on a screenshot):

Calculate the enthalpy for the following reaction:
2C(s) + H2(g) ---> C2H2(g) dH° = ? kJ

Given the following unbalanced thermochemical equations:
C2H2(g) + O2(g) ---> CO2(g) + H2O dH° = -2599 kJ
C(s) + O2(g) ---> CO2(g) dH° = -393.5 kJ
H2(g) + O2(g) ---> H2O(l) dH° = -571.6 kJ

Solution:
1) To get the target equation:
a) Balance all equations!
b) First eq: flip it so as to put C2H2 on the product side.
c) Second eq: multiply it by 4.
d) Third eq: do nothing. We need one H2 on the reactant side and that's what we have.

2) Rewrite all three equations with changes applied:
4CO2(g) + 2H2O(l) ---> 2C2H2(g) + 5O2(g) dH° = 2599 kJ
4C(s) + 4O2(g) ---> 4CO2(g) dH° = -1574 kJ
2H2(g) + O2(g) ---> 2H2O(l) dH° = -571.6 kJ
Notice that the dH° values changed as well.

3) Add up dH° values for our answer: (2599 kJ + (-1574 kJ) + (-571.6 kJ)/2 = +226.7 kJ