Physical & Chemical Changes ESSENTIAL QUESTION: How can you use evidence to determine if a change is physical or chemical? Objectives: Identify examples of chemical and physical changes and provide evidence that these changes are taking place. Defend the claim that mass is conserved in both physical and chemical reactions through investigations. Investigate the effect of temperature on the rate of chemical changes.

BELL RINGER Michael decides to bake bread one morning. He measures ingredients, mixes them other to make a dough, and cooks the dough in an oven. As the dough cooks, Michael observes the bread rising. Which of the following is evidence of the chemical change in Michael’s break-making process? A. Sugar dissolving in the liquid batter. B. The bread rising as carbon dioxide is released. C. Water in the dough being released as water vapor. D. The dry ingredients mixing with the wet ingredients.

PHYSICAL CHANGE Physical Changes result when there is a re-arrangement to the molecules of a substance. The molecules themselves stay the same. Ex: Changes in state of matter, shape, size, volume, mass, weight, and density.

CHEMICAL CHANGES Chemical changes occur when the molecules of a substance are broken apart and changed into a new substance with new properties. Ex: Bubbling and fizzing, light production, smoke, and presence of heat.

Key Indicators of Each Type of Change Physical Change Indicator Chemical Change Indicator Can be reversed. NO New Substances formed! Ex: Change to State of Matter. NEW Substance Formed! Can’t be reversed. Production of a NEW Color, Odor, Energy, Gas.

How Temperature Affects Chemical Reactions The rate of a chemical reaction will INCREASE when heat is added. The rate of a chemical reaction will DECREASE when heat is removed.

Law of Conservation of Mass Mass cannot be created or destroyed, just changed from one form to another.

BELL RINGER REVISITED Michael decides to bake bread one morning. He measures ingredients, mixes them other to make a dough, and cooks the dough in an oven. As the dough cooks, Michael observes the bread rising. Which of the following is evidence of the chemical change in Michael’s break-making process? A. Sugar dissolving in the liquid batter. B. The bread rising as carbon dioxide is released. * C. Water in the dough being released as water vapor. D. The dry ingredients mixing with the wet ingredients.

YOU DO TIME!

YOU DO #1 Four siblings did chores during the weekend. Ling cooked eggs. Gabe raked leaves. Chris sewed buttons. Briana dried laundry. Which of these involved a chemical change? A. Cooking eggs B. Raking leaves C. Sewing buttons D. Drying laundry Correct Answer: A

YOU DO #2 Anthony’s homework assignment is to demonstrate that an orange has already undergone a chemical change. Which of the following should he bring to class to best demonstrate a chemical change? A. Diced orange B. Rotten orange C. Peeled orange D. Mashed orange Correct Answer: B

YOU DO #3 Carlos stomps a soda can flat and throws it away. Which of the following statements BEST describes the change made in the soda can? The soda can kept the same mass as it changed in shape only. The soda can lost mass as it was changed into a smaller size. The soda can gained more mass because its shape changed. The soda can lost mass as it was crumpled and changed form. Correct Answer: A

EXIT TICKET How can you use evidence to determine if a change is physical or chemical?