Chapter Highlights and Notes Holt Chapter 15 Chapter Highlights and Notes
Section 1 Chemical reactions form new substances with different properties than the starting substances Properties such as presence of a gas, temperature change, color change, precipitate appears, odor develops, solid disappears, etc.
Clues that a chemical reaction is taking place include: - formation of a gas (often CO2) - formation of a solid - a color change - and energy change (heat produced -> hotter - or- heat removed -> colder)
A chemical formula tells the composition of a compound using chemical symbols and subscripts. Subscripts are small numbers to the right of a symbol in a formula. H2O (the 2 is a subscript) 2 atoms of H, 1 atom of O
Chemical formulas can sometimes be written from the names of covalent compounds and ionic compounds.
A chemical equation describes a reaction using formulas, symbols, and coefficients.
A balanced equation uses coefficients to illustrates the law of conservation of mass, that mass is neither created nor destroyed during a chemical reaction. The 2 in 2NaCl is the coefficient (there are 2 atoms of Na and 2 atoms of Cl)
Section 2 Many chemical reactions can be classified as one of four types by comparing reactants with products. Synthesis Single replacement Double replacement Decomposition
Synthesis reactions - the reactants form a single product 2H2 + O2 --> 2H2O
Single Replacement reactions A more-reactive element takes the place of a less-reactive element in a compound. Zn + 2HCl --> ZnCl2 + H2
Decomposition Reactions A single reactant breaks apart into two or more simpler products H2CO3 --> H2O + CO2
Double Replacement reaction Ions in two compounds switch places. A gas or precipitate is often formed NaCl + AgNO3 --> NaNO3 + AgCl
Section 3 Energy is released in exothermic reactions. The energy released can be written as a product in a chemical equation
Energy is absorbed in endothermic reactions. The energy absorbed can be written as a reactant in a chemical equation.
The law of conservation of energy states that energy is neither created nor destroyed.
Activation energy is the energy needed to start a chemical reaction.
Energy diagrams indicate: Exothermic - energy is given off Endothermic - energy is absorbed
The rate of a chemical reaction is affected by: - temperature - concentration - surface area - presence of catalyst - presence of inhibitor
To increase the rate of reaction: - Increase temperature and/or - increase concentration and/or - increase surface area and/or - add a catalyst
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