Final answer:
A double displacement reaction that evolves gas likely leads to the formation of a gaseous product and may exhibit a temperature change depending on the net moles of gas involved. The reaction could be decomposition if it breaks a compound into simpler substances including gas. Barium sulphate can be identified by its insolubility and the formation of a white precipitate.
Step-by-step explanation:
The question asks us to predict the products and classify the type of reaction in a scenario involving a double displacement reaction that evolves gas. The four visual clues indicating a chemical reaction are a change in color, production of a gas, formation of a precipitate, and a transfer of energy, indicating whether it's endothermic or exothermic.
For a gas-evolving reaction, we predict that the product formed will include a gaseous substance. Given the information, one can infer that when the reaction has a net loss of three moles of gas, it is indicative of a decrease in energy. Conversely, a net increase of seven moles of gas would suggest an increase in energy or temperature. This helps us understand the energy aspect of the reaction.
The reaction can be classified based on the products formed and the changes observed: A synthesis reaction involves combining elements or simpler compounds to form a complex compound. In contrast, decomposition involves a complex molecule breaking down into simpler substances. If the reaction resulted in the formation of a gas from reactants that did not contain it in a free state, then it's likely a decomposition reaction.
To identify barium sulphate as a product, you would perform a test involving its solubility properties, as barium sulphate is insoluble in water and would form a white precipitate.