dau coroana completatu spatile libere cu formele chimice ale reactantilor sau ale produsilor de reactie si stabileste cofecienti stometrici pentru ecuatile reactilor a).................H2+............O2---------》........... b)...........................+................CO2-----------》H2CO3 c )..........................+..............S-----------------》
d ............................. +.................N2------------- 》........NH3
e .................MgO+........-------------》...........Mg(OH)2