Chapter 7 Chemical Reactions

7.1 Notes Chemical reactions alter arrangements of atoms. A. Atoms interact in chemical reactions. ***Remember physical changes involve changes of state (ex. liquid to gas)but it still remains what it is; chemical changes cause substances to change into one or more different substances.

Different combinations make different substances!

1. chemical reaction- the process by which chemical changes occur; atoms are rearranged and chemical bonds are broken and formed. 2. Bonds are broken and formed when the particles of the original components collide with one another. 3. New arrangements form NEW substances! Example: Water can be broken apart by a process called electrolysis. An electric current changes the water (liquid) into the two different gases. Hydrogen and Oxygen are used for rocket fuel in space shuttles. During liftoff, liquid hydrogen an liquid oxygen are combined in a reverse electrolysis reaction. This produces water and large amounts of energy to push the shuttle into orbit.

Hydrogen and Oxygen are used for rocket fuel in space shuttles. During liftoff, liquid hydrogen and liquid oxygen are combined in a reverse electrolysis reaction. This produces water and large amounts of energy to push the shuttle into orbit.

1. Reactants – substances present at the beginning of a chemical reaction (bonds break) 2. Products- substances formed by a chemical reaction (new bonds form) 3. Reactants and products can be elements and/or compounds depending on the reaction taking place. MgSO 4 + Na 2 CO 3 2 Na + + SO 4- + MgCO 3 (solid) reactantsproducts yields

Color change Temperature change Formation of a solid (precipitate) Bubbles (gas) ODOR

1. Synthesis- a new compound is formed by the combination of simpler reactants A + B C 2. Decomposition- a reactant breaks down into simpler productsC A + B 3. Combustion- one reactant is always oxygen and the other often contains hydrogen and carbon CH 4 + 2O 2 CO H 2 O

Rusting iron may take months while striking a match is instant ! Three physical factors affect the rate of reaction: 1.Concentration 2.Surface Area 3.Temperature One chemical factor affects the rate of reaction: catalyst

1. Surface Area- increasing the surface area increases the number of particles that can react. Which cooks faster: an entire steak or pieces of beef tips? 2. Temperature- increasing temperature increases energy so particles move faster 3. Concentration- increasing the concentration (number of particles in a certain volume) increases the number of particles that can react.

catalyst- a substance that increases the rate of reaction but it itself is not consumed (remains unchanged) in the reaction Enzymes are catalysts in living things! Some are in your stomach to help digest food every time you eat!

7-2 Notes Law of Conservation of Mass

Matter can never be created or destroyed in a chemical reaction; mass of the reactants are equal to the mass of the products

Chemical reactions can be described by chemical equations. They represent how atoms are arranged in the chemical reaction. ***Left side-reactants ***Right side-products The number of atoms of each element in the equation must be the same on each side!

1. Reactants and Products 2. Atomic symbols and chemical formulas 3. Direction of the reaction C + O 2 CO 2 reactants product Direction of reaction subscript Chemical formula Atomic symbols

CH 4 + O 2 CO 2 + H 2 O UNBALANCED C- 1 carbon H- 4 hydrogen O- 2 oxygen C- 1 carbon H- 2 hydrogen O- 3 oxygen

You can balance a chemical equation by changing amount of products and reactants represented. You will use a coefficient to do so! Coefficient- number in front of the entire chemical formula, NOT between atoms!!! SUBSCRIPTS CAN NEVER BE CHANGED! Coefficients and subscripts can be multiplied to balance equations!

7-1/7-2Quiz 1.the process by which chemical changes occur; atoms are rearranged and chemical bonds are broken and formed. 2.substances present at the beginning of a chemical reaction 3.Matter can never be created or destroyed in a chemical reaction; mass of the reactants are equal to the mass of the products 4.number in front of the chemical formula 5.substances formed by a chemical reaction 6.a substance that increases the rate of reaction but it itself is not consumed (remains unchanged) in the reaction 7.List the four factors that affect the rate of reaction. 8.Distinguish between synthesis and decomposition reactions. 9.What three elements must be present for combustion to occur? B. chemical reaction C. Law of Conservation of MassA. Reactants D. Products E. Catalyst F. coefficient

You TRY! 1. Ca + O 2 → CaO 2. N 2 + H 2 → NH 3 3. Cu 2 O + C → Cu + CO 2

You TRY! 1.Ca + O 2 → CaO 2. N 2 + H 2 → NH 3 3. Cu 2 O + C → Cu + CO 2

7-3 Notes Energy Changes in Chemical Reactions

***Break bonds between reactants (requires energy) ***Form bonds between products (releases energy) Bond Energy- energy associated with bonds

Endothermic/Exothermic Reactions

Exothermic reaction- a reaction in which energy is released 1. can be observed during physical changes like freezing 2. produce an increase in temperature 3. energy of the reactants are less than the energies of the products Reactants Products + energy

4. energy is released as heat 5. combustion reactions are exothermic 6. some energy is released as light (like glow sticks) 7. Occur in living things (fireflies, bombardier beetle, fish, squid, jellyfish and shrimp)

endothermic reaction- a reaction in which energy is absorbed 1. Decrease in temperature 2. Energy of reactants are greater than energy of products 3. More energy is used to break the bonds of reactants 4. Energy is absorbed as heat from the surroundings Reactants + energy Products

5.Absorbs energy in other ways as well. (ex. electrical) ***photosynthesis -energy from sunlight is absorbed and turns CO2 and water into O2 and glucose (sugar)- stored glucose energy

Photosynthesis

7-4 Notes Chemical Reactions in Life and Industry

Forms of stored energy include fossil fuels and sugar glucose. ***Remember living things obtain glucose molecules (energy) by eating plants or other animals that have eaten plants. This occurs through respiration which is the reverse of photosynthesis or combustion of glucose!

The energy released by respiration can be used for growth of new cells, movement or any other life function. **Remember your body uses catalysts (enzymes) to break the glucose molecules into smaller pieces while other enzymes break bonds within each piece. This gives you energy you need from the stored food to run or etc.

Driving a car requires the “combustion” of gasoline! Chemical reactions that change a car’s exhaust gases use catalysts!

Some chemical reactions produce “unwanted waste” like carbon monoxide and nitric oxide from car engines!! These lower the efficiency of combustion. These gases react with water vapor to form smog and acid rain!

This is why the catalytic converter was created in the 1970’s! It was a solution to remove the “unwanted waste” from cars through another chemical reaction! They contain metal catalysts such as platinum, palladium and rhodium. Research is still being completed to improve them by using less expensive metals such as magnesium and zinc.

THINK ELECTRONICS! S emiconductors and electrical signals come from chemical reactions! Quartz is the source of silicon which is the 2 nd most abundant element on earth! It’s used as a semiconductor in electronics! It all came about in the 1950’s when they introduced microchips!

Video: Reaction Equations