chemical reactions ch 6. essential questions part 1 what is a chemical reaction? how can you…
DESCRIPTION
Properties Physical property – a characteristic of a pure substance that can be observed without changing it into another substance. Chemical property – a characteristic of a pure substance that describes its ability to change into a different substance.TRANSCRIPT
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Chemical Reactions
Ch 6
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Essential questions part 1What is a chemical reaction?
How can you tell a reaction has taken place?
What happens with energy in a chemical reaction?
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Properties
Physical property – a characteristic of a pure substance
that can be observed without changing it into another substance.
Chemical property – a characteristic of a pure substance
that describes its ability to change into a different substance.
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Changes
Physical change – a change in a substance that does not
change its identity.Chemical change – a change in which one or more
substances combine or break apart to form new substances.
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How does bonding create a chemical change?
chemical changes occur when bonds break and new bonds form.
Chemical reactions involve changes in properties and changes in energy that you can observe.
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Chemical reactions cause:
1.Bonds to break2.atoms to rearrange3.New bonds to form
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III. Evidence for chemical reactions
The process where one or
more substances change into one
or more DIFFERENT substances.
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clues that reactions occurred A gas is formed – bubbling or fizzing A solid is formed – precipitate (little chunks or
cloudiness forms) Color changes Energy (temp.) changes Odor changes Any change that is a result of a new substance
being formed
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Changes in Energy Endothermic – reaction that absorbs
energy into the bonds from the environment, gets colder Example: cooking
Exothermic – reaction that releases energy from the bonds to the environment – gets hotter Ex: fire (fast), explosion (fast), rust
(slow)
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Energy in Chemical Reactions
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Activation Energy: Energy used to start a reaction
Example: friction used to start a match Using a match to light a candle or
bunsen burner
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Compounds
Two or more elements that are chemically combined
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Types of Compounds: Review
1. Covalent – formed from 2 or more nonmetals that share electrons
2. Ionic – formed from a metal and a nonmetal that transfer electrons to form charged ions
3. Metallic –formed when two metals share loose electrons between many positive metal ions
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Describing Chemical Reactions Essential Questions 6.2
How do you describe a chemical reaction?
How is matter conserved during a reaction?
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How to represent:
Element – symbolCompound – formula
Reaction – equation
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Chemical Formula -short way to write the name of a compound
1. Tells – what kind of elements make up the compound(Look for symbols)
2. Tells – how many atoms of each element there are
3. Subscript – small number written below and after the symbol to tell how many atoms there are of that element. If there is no subscript, then there is 1 atom
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Parts of an equationReactants – a substance that undergoes change in a chemical reaction.
Products – a substance formed as a result of a chemical reaction.
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Formulas for covalent compounds When naming a covalent compound, a
prefix is always used on the 2nd element to indicate the number of atoms of the element in the compound.di – two tri – three mono – one
Carbon dioxide Carbon monoxide
Dihydrogen monoxide
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D. Formulas for ionic compounds The formulas must have a neutral
charge (total charge of zero). Positive and negative charges must be
equal Magnesuim fluoride MgF2
Mg+2 2 F -1
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Describing Chemical Reactions
What are chemical equations? Uses symbols and formulas to show
what happens in a chemical reaction
Ex: NaOH + HCl NaCl + H2O
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2. Parts of an Equationa. Reactant
(NaOH and HCl)
b. Product(NaCl and H2O)
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Traits of Chemical Reactions
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2. Parts of an Equation
c. Arrow Means “produces” or “yields”.It tells you a reaction has taken place.
d. Plus Sign Separates 2 or more elements or compounds in the reactant or product.
e. Coefficient Number in front of the element or formula; it tells how
many molecules there are.2HO
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Chemical Equations
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6.3 Controlling chemical reactions Essential questions
What is the Law of Conservation of Matter/Mass?
How can you control the rate of a reaction?
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V. Law of Conservation of Matter:
Matter or energy cannot be created or destroyed, - it only changes form
All atoms you started with in the equation are there at the end of the reaction, just REARRANGED
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How to balance an equation: CH4 + O2 CO2 + H2O 1. List each element and the number of atoms
C = 1 C = 1 H = 4 H = 2 O = 2 O = 3
2. Add a COEFFICIENT to balance the atoms on each side
CH4 +2 O2 CO2 + 2 H2O C = 1 C = 1 H = 4 H = 4 O = 4 O = 4
3. RECHECK the number of atoms on each side of the equation.
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VII. Rate of Chemical Reactions How fast or slow a chemical reaction occurs depends on:
1. How hard the molecules bump into each other
2. How many times the molecules bump into each other
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Things that affect reaction rate:
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VIII. Rates of chemical reactions: 1. Surface area – higher surface area= faster
reaction lower surface area = slower reaction 2. Temperature –higher temperature = faster
reaction lower temp.= slower reaction
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Things that affect reaction rates 3. Concentration – higher concentrations =
faster reactions lower concent. = slower reaction 4. Catalyst: a substance that affects the rate of
the reaction without being changed by the reaction Ex. Chlorophyll (speeds up reaction)
5. Inhibitors – a material that decreases the rate of a chemical reaction. (slows down reaction