Question

Cherylanne mixes together Chemical A and Chemical B in a test tube, forming Chemical C. The mixture instantly turns cool to the touch. She then adds Chemical D, and the reaction becomes hot and explodes.

What can be known about this situation?

Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction.
Chemicals A and B form an exothermic reaction, and chemicals C and D form an endothermic reaction.
Chemicals A and C form an endothermic reaction, and chemicals B and D form an exothermic reaction.
Chemicals A and B form an exothermic reaction, and chemicals B and D form an endothermic reaction.

Answer 1

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❒ First reaction:

Reaction between two substances A and B. It was observed that the mixture or the product formed was cold instantly. This means,

• The temperature at the beginning was higher than the temperature later on.

• The energy of reactants was more than energy of products.

• Some amount Heat energy was used up in the reaction which lowered the temp.

As the energy was taken in, it was an endothermic reaction. The Chemicals A and B form an endothermic reaction.

❒ Second reaction:

Now the product of the above reaction is Chemical C which is again reacted with another Chemical D. And it was observed that the mixture was hot and resulted into a sudden explosion. This means,

• The temperature at the end was higher than the temperature at the beginning.

• The energy of products was more than energy of reactants.

• Energy is provided to the reaction externally to reach the required amount.

As the energy was given out and resulted in hot explosion, the reaction was exothermic reaction. The Chemicals C and D form an exothermic reaction.

❒ According to options:

Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction. (Option A) is the correct alternative✓.

Answer 2

We know that Cherylanne did not take proper safety procedures. Nah, I'm kidding.

• The answer would be A, since Endothermic reactions feel cold to the touch, while exothermic reactions feel hot to the touch.

• In the reaction that feels hot and explodes, A and B reactants are all gone, having been reacted together to form C, which is what reacted with D to explode.

Answer:

Option A. is correct

• Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction.