Chemical Reactions and Equations

Symbols of Physical State

Writing the symbols of physical states:

Symbols of physical states of elements or compounds present in reactants and product are written to make the chemical equations more informative.

Symbols used to denote the physical states of elements and compounds:

For solid state : s [Small 's' is written in bracket () after the element or compound to show the solid state.]

For liquid state: l [Small 'l' is written in bracket () after the element or compound to show the liquid state.]

For gaseous state: g [Small 'g' is written in bracket () after the element or compound to show the solid state.]

For aqueous solution: 'aq' ['aq' is written in bracket after the compound to show the solution in water. This means ‘aq’ denote the aqueous solution.]

In the chemical equation given above, small 's' has been written after Zn(zinc). This says that Zinc is in solid state.

Small ‘l’ has been written after Sulphuric acid (H₂SO₄). This says that sulphuric acid is in liquid state.

Small ‘aq’ has been written after zinc sulphate (ZnSO₄). This says that zinc sulphate is in aqueous solution. However, we get the precipitate of zinc sulphate in the above reaction, so small ‘s’ to denote solid state is written after zinc sulphate. But it is better to write (aq) after zinc sulphate to denote its solution in water.

Small ‘g’ has been written after H₃ (hydrogen). This says that Hydrogen is in the gaseous state.

Example: 2:

Example: 3:

Writing the condition in chemical equation

Some reactions take place in particular conditions, such as temperature, pressure and catalyst. These conditions are generally written above or below the arrow in a chemical equation.

Example: Reaction for making of food by plants.

Plants make their food (glucose) in the presence of sunlight and chlorophyll. Chlorophyll is green pigment like substance which is found in the leaves of plant. Because of presence of chlorophyll leaves of plant look green.

Here, ‘sunlight’ and ‘chlorophyll’ has been written above and below the arrow respectively. This tells that reaction takes place in the presence of sunlight and chlorophyll.

Example:

Reaction of carbon monoxide with hydrogen gas at an atmospheric pressure of 340.

Here, this reaction takes place at 340 atm. And this has been written above the arrow.