When reactants are in different states of matter the reaction is called heterogeneous.
Example: CaCO3 (solid) + H2SO4 (liquid) = CaSO4 (s)+ H2O(l) + CO2(g)
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Heterogeneous matter has parts with different characteristics.
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Heterogenous mixture
A heterogeneous mixture is composed of two or more components that are not evenly distributed and are easily observable. An example of a heterogeneous mixture is beef stew.
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In homogenous reaction all the components/reactants taking part in the reaction form one single phase, with the reaction occurring in the bulk of this system. In heterogeneous reaction all the components/reactants taking part in the reaction are in different phases, with the reaction occurring between the delimiting surface of the components/reactants.
An example would be a mixture of flour and water. Heterogeneous mixtures have two different phases.