Hello Chemical Forums! I was recently doing some online homework for my Chemistry class and stumbled upon a multiple choice question which, to me, had more than one answer. Here's the question:
A white solid is mixed with a clear liquid in a beaker. The mixture fizzes, turns green, and the beaker feels hot to the touch. What kind of change is occurring, and why?
Here are the answers I can choose from:
A. A physical change because the color changed, and color is a physical property.
B. A chemical change because an energy change is observed.
C. A chemical change because new substances are being formed that have new physical properties
The system marks A and B as incorrect, and C as the correct answer. However, I believe both B and C are correct.
Here's my reasoning for B:
If a sudden increase in temperature were to occur from the beaker when mixing a white solid into a clear liquid, it would be safe to assume that the reaction is exothermic (releasing energy into the surroundings). This would mean bonds are making products - a chemical interaction.
reactants → products + energy.
A physical change cannot suddenly release heat without first having heat inputted. It depends on the temperature and pressure of the surroundings.
Is my reasoning correct?
If not, how can a physical reaction produce heat when mixing two substances? - if possible, would you be able to give an example?
Thank you, everyone!