Question

When a chemical reaction take place how do we know in which colour has it changed?

For example-
Zn+CuSO4 --> ZnSO4+Cu

So what will be the colour change. How do we get to know that?​

Answer 1

our question has to be more specific and clearer, Mixing Zinc Metal with Solid Copper Sulphate will have NO reaction, But assuming the Copper Sulphate is in Aqueous/Molten State, The Zinc reacts with Copper Sulphate/Sulfate.

It will undergo a Redox Reaction ,called the Displacement Reaction of Metal because Zinc is More Reactive than Copper according to the Reactivity Series. It WILL NOT react if both are in Solid State , Your question has to be clearer.

But firstly it depends on what is the oxidation state of the Copper since Copper is a Transition Metal and have varying Oxidation State. There is Copper (I) and Copper (II) and even Copper (III) . Also ,the Copper Sulphate has to be in Aqueous State ,dissolved in water in order for the reaction to occur , so in order to get the Dry sample (Anhydrous Salt) , You will have to use Evaporation To Dryness , if not , Crystallisation to get the Hydrated Copper Sulphate Crystals.

So assuming you are talking about Copper(II) Sulphate , The Full Chemical equation would be as follows

Zinc + Copper (II) Sulfate → Copper Metal + Zinc Sulfate

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

The Copper form will be the Reddish Brown deposit and the Copper II Sulphate Solution will become less blue (Paler)

The Ionic Equation is

Zn (s) + Cu²⁺ (aq) → Zn²⁺ (aq) + Cu (s)

Change in Free Energy: ΔG(20C) = -206.6kJ

Change in Enthalpy: ΔH(20C) = -208.8kJ (Exothermic Reaction)

Hope I’ve answered your question , Please correct me if I’m wrong , Have a Nice day!