For which of the following cases is there a clear indication that a chemical reaction is taking place?Case 1:  Two clear, colorless liquids at 19.5 degrees Celsius are combined in a test tube.  A few seconds later, the contents of the test tube appear to be a clear, colorless liquid with a temperature of 19.8 degrees Celsius.Case 2:  Two clear, colorless liquids at 24.3 degrees Celsius are combined in a test tube.  A few seconds later, the contents of the test tube appear to be a clear, colorless liquid with a temperature of 32.9 degrees Celsius.

According to the pre-lab presentation, which of the following is a reason for a "false positive" conclusion that a chemical reaction occurred in the test tube?Group of answer choicesTwo clear colorless liquids are combined and produce no visual change (still a clear colorless liquid) when the test tube is agitated.Bubbles are observed after the test tube is agitated.An odor is generated when the test tube is agitated.A red color in the test tube changes to a blue color after the test tube is agitated.

Which answer would provide the most detailed and accurate description of the observations for this reaction?Group of answer choicesThe test tube contains both a white, cloudy liquid and a clear, colorless liquid.The test tube contains a white liquid and a clear, colorless solid.The test tube contains a white solid floating in a clear, colorless liquid.The test tube contains a clear, colorless liquid with a white solid that has sunk to the bottom.

How do you know a chemical reaction has taken place?

A scientist obtains a mixture of methane and oxygen in a closed opaque vessel. She knows that a mixture of methane and oxygen is a clear gas. She then follows these steps:Light a fuse to provide a spark inside of the vessel.Carefully extract the gas out the vessel directly into a large sealed test tube.Observe the gas in the test tube.Determine whether or not a chemical reaction occurred after lighting the fuse.The scientist sees that the gas in the test tube is still a clear gas. How can the scientist determine whether or not a chemical reaction occurred in the test tube? A. by observing the color of the gases in the test tube and comparing them to those of methane and oxygen B. by testing the boiling points of the gases in the test tube and comparing them to those of methane and oxygen C. by determining whether or not a phase change occurred because the fuse was sparked D. by determining whether or not mass of matter was gained because the fuse was sparked

A student observed a precipitate form during a chemical reaction. Which of the following did the student most likely observe? A. Bubbles of gas floated to the top of a solution. B. The color of a liquid changed when a solid was added to it. C. Steam rose from a flask when a powder was added to a liquid. D. A solid sank to the bottom of a container when two liquids were mixed.