EXPERIMENT: OBSERVATION OF A PHASE CHANGE How do you know when a substance is boiling? Is it when you first see little bubbles? Is it when the thermometer shows a certain temperature? Is there a better way to tell? In this activity, you will observe the changes in water as it transforms from ice to liquid water and then begins to boil. Part of your task is to determine exactly when it is boiling. You will be able to see that during a change of state, the energy put into a substance to rearrange the structure of the substance, or change its phase, not to change its temperature. The energy used in this manner is called latent energy. OBJECTIVES Use your knowledge of changes of state to hypothesize how you will determine when the water sample is boiling. Do a graphical analysis of data provided from an example experiment. Interpret graphical information with respect to changes of state and latent energy. Online Lab The animation below shows you the main stages of this experiment. Before you watch the animation, write a hypothesis about when a substance is boiling, using the “if … then … “format. Once you have recorded your hypothesis, watch the animation. SHOW TRANSCRIPT Present Your Findings Here is the data sheet with all of the data collected during the experiment presented in the animation. Click here to see an example of the data sheet Use this data to graph temperature vs. time. This will be a phase diagram. You may use a graphing program or graph the data by hand and scan to submit. In the essay box below, write a summary paragraph discussing this experiment and the results. Use the following questions to help guide the content of your paragraph. What was your hypothesis? According to your data, do you think your hypothesis was correct? What is latent heat? How does it show up on a phase diagram? When a substance is absorbing latent heat, what is happening to it? According to the data, what are the melting and boiling points of water? How can you tell? What practical applications are there for this procedure?