The equation for the reversible reaction between hydrogen and iodine is to form hydrogen iodide is shown.
the colours of the reactants and products are shown.
h2(g) + i2(g) < --> 2hi(g)
colourless + purple< --> colourless
the forward reaction is exothermic.
which statement is correct?
a) an increase in pressure has no effect on the equilibrium position.
b) the purple colour fades when the reaction mixture is heated.
c) when equilibrium is reached, both forward and reverse reactions stop.
d) when more hydrogen gas is added, the purple colour increases.

it should be p1 v1 = p2 v2

  the   balanced   equation   for   reaction of   ca metal   with   o2 to   produce   cao   is as below

2 ca+ o2→ 2 cao2

  explanation

the reaction is   balanced     since the   number of atoms   in reactant side is   equal to   number of atoms   in   product side.   for   example   they   are 2   atom of   ca in   reactant   side   and   2   atoms of ca   in   the product side.

  the   process   is a   meet the   requirement   of   redox   reaction because :     calcium   is   oxidized   from   oxidation state 0   to 2+   while   oxygen   is reduced from   oxidation   state   0   to 2-

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.