so...hmm....?

Question

A sample of lauric acid was heated above its melting point in a test tube and then cooled in a bath of water until it solidified. The termperature of the acid was measured as a function of time

Then they show a temp-time graph the starts up around 62 C and drops to 46 C and remains at a constant temp for the rest of the graph

1. what is the physical meaning of the flat region on the graph?
is it just that the temperature of the acid at the time is constant and the acid is changing state?

2. Use the graph to estimate the melting point.

Would it just be the 46 C where the graph starts going constant?

3. Is heat being absorbed or released as it solidifies?

I put released since it says it is cooled in a bath of water...meaning the heat goes to the surroundings.

Can you just tell me if thats correct

Answer 1

You are essentially correct. These questions are the attempt of the textbook author to help you understand the difference between "temperature" as measuered by a thermometer and "heat" as an absolute measure.

The actual value of lauric acid's melting pt/freezing pt is a little lower, perhaps the graph is set up to look more like one students might make -- 2 degrees of error is not far off.

I might clarify that the heat is leaving the sample of lauric acid and is warming the water bath. 46 degress celsius is about 115 degrees fahrenheit, still much warmer than your body temp....