d escribing c hemical r eactions chapter 6 section 2
TRANSCRIPT
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DESCRIBING CHEMICAL REACTIONS
Chapter 6 Section 2
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WHAT ARE CHEMICAL EQUATIONS?
Is a short, easy way to show a chemical reaction, using symbols instead of words.
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Uses chemical formulas with subscripts and coefficients to summarize a reaction
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A formula is a combination of symbols that represents elements in the compound
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The substances at the left of the equation are called reactants, when the reaction is complete, on the right you have products.
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If you have two or more reactants or products they are separated by a + sign
Reactant 1 + reactant 2 ----> Product 1 + product 2
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CONVERSION OF MASS
During a chemical reaction, matter is neither created nor destroyed, it just changes form.
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All the atoms present at the start of the reaction are present at the end
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The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products
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OPEN AND CLOSED SYSTEMS
Open: matter can enter from or escape to the surroundings.
Burning match
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Closed: matter is not allowed to enter or leave the system
Eg: reaction is sealed in a plastic bag
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BALANCING CHEMICAL EQUATIONS
To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation
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4 Step process
Step 1: Write the equation: Reactants on the Left, products on the right
___H₂ + ___O₂ ----> ____H₂0
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Step 2: Count the number of atoms of each element on each side of the equation
2 hydrogen, 2 oxygen on the react side, 1 oxygen and 2 hydrogen on the product side. IF THE ATOMS DO NOT EQUAL GO TO STEP 3
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Step 3: Use coefficients to balance atoms
A coefficient is a number placed in front of a chemical formula. It is multiplied by the subscript to get the new number of atoms
Always check both sides when using a coefficient
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Step 4: Check your work
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CLASSIFYING CHEMICAL REACTIONS
Synthesis: when 2 or more elements or compounds combine to make a more complex substance
2H₂ + O₂ ---> 2 H₂O
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Decomposition: Breaks down compounds into simpler products
2H₂O₂ ----> 2H₂O + O₂
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Replacement: When one element replaces another element in a compound or when 2 elements in different compounds trade places
2CuO + C ----> 4 Cu + CO₂FeS + 2 HCl ----> FeCl₂ + H₂S