During an experiment, Mr. Lehman tells his students to be alert for signs that an endothermic reaction is happening. Which of the following scenarios would his students most likely observe? A test tube becomes cool to the touch. A liquid appears to glow. A new odor comes from a beaker. A solid forms from a mixture of solutions.

The endothermic reaction can be observed by the cooling down of the test tube. The test tube has been cooled down by the absorption of the energy from the surrounding by the reaction mixture.

The endothermic reactions are the one that utilizes the energy from the surrounding for the completion of the reaction. The endothermic reaction will result in the decreasing of the temperature of the system as the surrounding energy has been absorbed by the reaction.

The system absorbs the surrounding energy, so there will be a -ve change in the enthalpy of the reaction mixture. Thus, when the reaction tube has been touched the temperature of the tube has been cooled down.

The liquid appears to glow when the incandescence phenomenon has taken place. The glowing liquid will be the resultant of the incandescence reaction.

The change in the odor has been depicting the formation of the product that has a smell. It has not been concerned with the type of reaction.

The formation of solids in the mixture has been the synthesis reaction. Or the change in the reaction condition has been the reason for the solid formation.

Thus, the endothermic reaction can be observed by the cooling down of the test tube.

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