Unit B Chemistry Week 3

chemcial reactions

I Can… Understand and describe exothermic and endothermic reactions Identify conditions affecting reaction rates

Remember How do we know If a chemical reaction/change has taken place? What is our main indicator of a chemical reaction occurring?

Chemical Reactions A chemical reaction takes place when two or more substances combine to form a new substance.

Terms to know Reactants- the materials at the start of the reaction Products- the new materials produced by the reaction Reactants always appear on the left side of the arrow wood+ oxygen----- carbon dioxide+ water+ energy

More examples of reactants and products 2NaCl 2Na+Cl2 How many atoms of each element are in the reaction? Reactants? Products?

Recall When a chemical reaction takes place evidence of the reaction may include the following: A colour change The formation of an odour The formation of a solid or a gas The release or absorption of heat

Exothermic A chemical reaction that releases heat energy into the surroundings. What does this mean in regards to temperature surrounding the experiment? Example: Our bodies and Ms Nielsen Demo

Endothermic A chemical reaction that absorbs heat energy What does this mean in regards to the temperature surrounding the experiment? Example: Ice Pack and Ms. Nielsen Demo

Ms Deanne demo KOH in Water NaCl on Ice Starting Observations? 24 degrees End of Experiment observations? 30 degrees Conclusions - Exothermic NaCl on Ice Starting Observations? 5 degrees End of Experiment observations? -7 degrees Celsius Conclusions - Endothermic Which is Endothermic? Which is Exothermic?

Chemical Changes Involving Oxygen Corrosion- a slow chemical change that occurs when oxygen in the air reacts with metal Ex. Rusting Combustion- a chemical reaction that occurs when oxygen reacts with a substance to form a new substance and give off energy Ex. Burning wood or gasoline

Chemical Changes Involving Oxygen Cellular Respiration- a chemical reaction that takes place in the cells in your body Ex. Glucose + Oxygen  carbon dioxide + water + energy Photosynthesis – a reaction that occurs in plants to create glucose Ex. Carbon dioxide + water + energy  Glucose + Oxygen Neutralization – when an acid and a base react to form water and a salt Ex. NaOH + HCl  NaCl + H20

Conservation of Mass in Chemical Reactions

I Can… Identify conditions affecting reaction rates Describe the law of conservation of mass

Conservation of Mass In a chemical reaction, products are formed when the reactants undergo a change These products usually look very different from the reactants, however the total mass of these products is always the same as the total mass of the reactants. The Law of Conservation of Mass states that matter is not created or destroyed in a chemical reaction.

Example 24.3 g of magnesium and 32.1 g of sulfur creates a new substance called magnesium sulfide. What will the mass of this be? No exception to this law has ever been found!

Systems Closed system- where no additional material is allowed to enter or leave Open system- where materials may escape

Factors Affecting the Rate of a Chemical Reaction

Factors 1) The presence of a catalyst 2) The concentration of the reactants 3) The temperature of the reactants 4) The surface area of the reactants

Catalyst Catalysts are substances that help a reaction proceed faster They are present, but are not consumed during the reaction Many reactions, such as breaking down food, require a catalyst called an enzyme. Enzymes can also help get rid of poisons in the body quickly. Ex. Catalase breaks down Hydrogen Peroxide, which is poisonous, into water and oxygen. https://www.youtube.com/watch?v=OttRV5ykP7A

Concentration The greater the concentration of the reactants, the faster the reaction. The increased concentration of the reactants means that there are more atoms of each reactant available to react.

Temperature The more heat added to the reactants, the faster the reaction. The added heat causes the atoms of each reactant to move faster, which increases the chances of colliding with each other.

Surface Area Increasing the surface area of the reactants means that more area is available for reaction.