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