Signs of a Chemical Reaction Unit 6 – Chemical Reactions

Physical Changes Physical change: Something where the shape of the object has changed – such as crushing a can of soda, breaking a piece of wood, tearing a piece of paper in half, turning water from ice to water to steam (states of matter) It doesn’t change the arrangement of the atoms, still the same substance before and after.

How can I cause a physical change? To this piece of paper?

Chemical Changes Chemical change: The atomic arrangement has changed – where chemical bonds are broken/formed Things such as burning causes chemical changes. The object before isn’t the same as the object after.

Quick Quiz Time: What is the difference between a chemical and a physical change? Is the following a chemical or a physical change? Why? water evaporates into steam Food is digested in the stomach A piece of cork cut in half

PAUL IS SMART: READING 2X Which of the following is an example of a physical change but not a chemical change? A. a log gives off heat and light as it burns B. a tree stores energy from the Sun in its fruit C. a penny lost in the grass slowly changes color D. a water pipe freezes and cracks on a cold night

What is a chemical reaction? When one or more new substances are formed When bonds are broken or formed

Well, how do we know a chemical reaction formed? There are 4 signs of a chemical reaction: Gas formation Temperature change Color change Solid formation

Gas formation When different solutions are combined and “bubbles” are produced, we know a chemical reaction occurred!

More examples Another example of gas formation

Temperature Change When the temperature of the reaction increases or decreases throughout the chemical reaction

Color Change When two solutions are mixed, the product has a different color than the original reactants.

Solid Formation When a new solid is formed when two solutions are mixed together

Ex. Glow Sticks

Quick Review – Don’t look at your notes! What are the four signs of a chemical reaction? What is a physical change?

Practice Question: Which of the following is a characteristic of all chemical changes? A. a different state of matter is produced B. some mass is converted to energy C. some form of light is given off D. a new material is formed

Brainpop:Conservation of Matter Who is the scientist that discovered the law of conservation of matter? How can you explain in your own words the law of conservation of matter?

The big picture… Just like the Law of Conservation of Energy states, energy cannot be created nor destroyed… The Law of Conservation of Matter states – matter cannot be created nor destroyed

The scientists behind the Law Antoine Lavoisier proposed the law of conservation of matter: Mass of the reactants = mass of the products Lavoisier based his law on the atomic theory proposed by John Dalton Which atomic model did John Dalton propose? The atom is a solid sphere with no smaller particles