Title: Conservation of Mass Activity 25 Title: Conservation of Mass

What is mass? How much matter is in something. The greater the mass, the more of the substance you have.

In activity 19, “Creating New Materials,” you cross-linked polyvinyl alcohol in a chemical reaction that produced a new polymer. Whether you are cooking your dinner in a pan or releasing energy from food in your cells, chemical reactions are changing reactants into products. How does the total mass of the reactants compare to the total mass of the products in a chemical reaction?

Vocabulary Atom- the smallest particle of matter Reactants- the molecules at the start of a reaction Products- the molecules at the end of a reaction Conservation- to keep the same amount

} Reactants Create molecules Make the following: One C3H8 Five O2 reactants products How many molecules of each product can you make with the reactants? } Reactants How many atoms? How many atoms? Reaction: C3H8 + 5O2 ___CO2 + ___H2O 3 4 21 atoms in the reactants & in the products

Law of Conservation of Mass States that atoms are not created nor destroyed during chemical reactions. All atoms in the reactants are also found in the products of a reaction. The total mass of the reactants is equal to the total mass of the products.

Which system is a closed system, and which is an open system? Open System: the contents of the jar can mix with the air surrounding the outside of the jar. Closed System: the chemical reaction is contained inside of the jar - all reactants and products stay in the jar.

Can of Soda When it is sealed, it is a closed system. When it is opened and the gases are released it is an open system with the air around the can.

What type of system is a person - open or closed? Open System - we take in food, oxygen, and water, from outside our bodies and excrete waste, carbon dioxide, and other substances. In reality, there are very few absolutely closed systems in our universe. Our planet, for example, is an open system in that it exchanges mass with the solar system and galaxy.

Chemical Reactions Signs of a Chemical Reaction: Change in Color of Products Production of Gas Emission of Light or Heat Appearance of a New Solid (Precipitate) or Liquid. These changes in physical appearance or characteristics of the reactants are a way to visually detect a chemical change. Change at the atomic level is not visible directly.

Demonstration: Closed System Sodium hydrogen phosphate in the bottle and copper chloride solution in the dropper. What do you think will happen to the mass of the system - the bottle and reactants - as the reaction occurs? Will it increase, decrease, or stay the same?

What evidence have you observed that indicates a chemical reaction occurred? Formation of a new substance Change in color of the solution What happened to the mass?

Law of Conservation of Mass Mass cannot be created or destroyed in a chemical reaction, but it can change form. The number of atoms do not change, they are simply rearranged. Mass stays the same in an open system and a closed system, but in an open system, the gas can escape.

What can you conclude about the effect of a chemical reaction on the mass of reactants in a closed system? The Law of Conservation of Mass goes against our perception of what we experience every day. When we observe food cooking or wood burning, it appears that mass is lost. This is because one of the products formed in these reactions is a gas we cannot see. If we could collect all of the gas and water produced when cooking or burning, we would find that mass is conserved.