LON-CAPA Writing Formulas and Chemical Equations in LON-CAPA

Using the Reaction Editor to Write Formulas or Equations

To enter chemical formulas as answers, subscripts are written as numbers following each element, and superscripts are preceded by the '^' symbol and followed by a space. For a superscript charge, the number should precede the charge. For example the ammonium complex of the cupric ion, [Cu(NH₃)₄]²⁺ would be written as [Cu(NH3)4]^2+. The "dot" in a hydrate formula is just entered as a period. For example MgCl₂•6H₂O would be entered as MgCl2.6H2O.

For the designation of an isotope, the superscripted mass number is preceded by '^', followed by a space, and the next number is subscripted as the atomic number. For example the helium ion, ⁴₂He²⁺ would be entered as ^4 2He^2+

To enter chemical equations, the reactants and products are preceded by their coefficients and separated by ' +' signs (leading space is necessary), and the reaction arrow is entered as '->' (a hyphen followed by a greater than sign). States can be indicated in parenthesis following the formula if requested in the problem.

The order of the reactants or products does not matter, but the reactants must come before the arrow and the products after the arrow. For example the complete combustion of methane could be entered in any of the following ways:

CH4 + 2O2 -> CO2 + 2H2O

CH4 + 2O2 -> 2H2O + CO2

2O2 + CH4 -> CO2 + 2H2O

2O2 + CH4 -> 2H2O + CO2

The Reaction Editor can be used to check that entries are correct. By clicking on the Edit Answer button, a pop-up window appears in which the formula or equation can be entered. Here is a screen shot of the window checking the entry of the equation:

3Sn(s) + Cr2O7^2-(aq) + 14H^+(aq) -> 3Sn^2+(aq) + 2Cr^3+(aq) + 7H2O(l)

Clicking the Check button next to the entry causes the formula or equation to be displayed above the line in proper format. Clicking the Help button provides a summary of these formatting conventions. If the formatted formula or equation appears correct, then clicking on the Insert Answer button puts the equation into the answer box of the problem and the Submit button in the problem submits the answer for grading.

Sometimes a question may already contain part of the equation in the Reaction Editor. In that case the equation should be completed without removing the part already entered.

The Reaction Editor tool was developed by Guy Ashkenazi, The Hebrew University, Jerusalem, ISRAEL.