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Questions and Answers
A chemical reaction is the transformation of one or more _______ into different substances.
A chemical reaction is the transformation of one or more _______ into different substances.
substances
Which of the following is NOT a definite evidence of a chemical reaction?
Which of the following is NOT a definite evidence of a chemical reaction?
A lit splint will glow brightly in the presence of carbon dioxide.
A lit splint will glow brightly in the presence of carbon dioxide.
False
What does the law of conservation of matter state?
What does the law of conservation of matter state?
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What is the most common form of sulfur?
What is the most common form of sulfur?
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In a chemical equation, the substances on the left side of the arrow are called _________, and the substances on the right side are called _________.
In a chemical equation, the substances on the left side of the arrow are called _________, and the substances on the right side are called _________.
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Subscripts in a chemical formula can be changed to balance a chemical equation.
Subscripts in a chemical formula can be changed to balance a chemical equation.
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What type of reaction is represented by the following general equation: AB → A + B?
What type of reaction is represented by the following general equation: AB → A + B?
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In a single displacement reaction, one element replaces another in a _________.
In a single displacement reaction, one element replaces another in a _________.
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All acid-base reactions are also considered double displacement reactions.
All acid-base reactions are also considered double displacement reactions.
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What is a precipitate?
What is a precipitate?
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Redox reactions involve the transfer of electrons.
Redox reactions involve the transfer of electrons.
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Which of the following is NOT a characteristic of combustion reactions?
Which of the following is NOT a characteristic of combustion reactions?
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The limiting reactant in a chemical reaction is the reactant that gets completely _________ during the reaction.
The limiting reactant in a chemical reaction is the reactant that gets completely _________ during the reaction.
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What is the theoretical yield of a reaction?
What is the theoretical yield of a reaction?
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What is the actual yield of a reaction?
What is the actual yield of a reaction?
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How is percent yield calculated?
How is percent yield calculated?
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Study Notes
Chemical Reactions
- Chemical reactions involve the transformation of one or more substances into different ones.
- This change alters the arrangement of atoms and molecules.
- Chemical reactions are evidenced by various observations, including color change, solid formation, gas evolution, absorption/emission of heat, or light emission.
- However, these are not always definitive.
- Sometimes, a reaction occurs without apparent signs.
Evidence of Chemical Reactions
- Color change
- Formation of a solid
- Formation of a gas
- Absorption/emission of heat
- Light emission
Lab Evidence in Chemical Reactions
- Wooden splint test: A "lit" splint is used to test for hydrogen (flammable), carbon dioxide (causes the splint to extinguish), or oxygen (keeps the splint burning).
- pH indicator (phenolphthalein): This indicator turns pink in the presence of hydroxide ions, which signals a basic solution. It is colorless in neutral or acidic solutions.
Law of Conservation of Matter and Mass
- Matter and mass are neither created nor destroyed in a chemical reaction.
- The total mass of reactants equals the total mass of products.
- Example: Water decomposing into hydrogen and oxygen, the mass of water equals the mass of hydrogen and oxygen combined.
- Example: Butane reacting with oxygen. Mass of butane and oxygen reacted must equal the mass of carbon dioxide and water formed.
Chemical Equations
- Chemical equations represent chemical reactions.
- Reactants (on the left side of the equation) give way to products (on the right side).
- Use reaction arrows to connect reactants to products.
- States of matter (s, l, g, aq) are written in parentheses.
Diatomic Elements
- Some elements naturally exist as diatomic molecules (two atoms bonded together).
- These elements are: hydrogen (H₂), oxygen (O₂), fluorine (F₂), chlorine (Cl₂), bromine (Br₂), iodine (I₂), and nitrogen (N₂).
- Remember these diatomic elements (HOFBrINCl) when writing equations.
Chemical Equations (continued)
- Chemical equations must be balanced (conservation of matter).
- Coefficients (numbers in front of compounds) determine the number of molecules
- Subscripts(numbers below elements in formulas) do not change when balancing.
Balancing Guidelines
- Balance elements that appear in only one compound on either side first.
- Balance metal atoms before nonmetal atoms.
- Treat polyatomic ions as units when balancing.
Writing/Balancing Reactions
- Write the skeleton equation.
- Place correct formulas on the correct sides.
- Use coefficients to balance the equation.
Correct Formulas and States of Matter
- Ionic compounds must be neutral.
- Molecular compounds have prefixes.
- States of matter are important for correctness.
- Consider common experiences (state of matter at room temp, etc.)
- Acids are aqueous (aq).
- Solubility rules are essential for aqueous compounds (are they soluble or insoluble? e.g. (aq) or (s)).
Aqueous Solutions
- Aqueous solutions are homogeneous mixtures where a substance is dissolved in water.
- Water molecules pull ions apart (NaCl) due to stronger attractions than between ions, creating solutions.
- Ionic compounds dissociate into their separate ions when dissolved in water (NaCl → Na+ + Cl–).
- Polyatomic ions remain intact when dissolved in water (e.g., NaNO3 → Na+ + NO3−).
Ionic Compound Solubility
- Insoluble ionic compounds form precipitates in solutions.
- Solubility rules dictate which ionic compounds are soluble or insoluble.
Classifying Reactions (continued)
- Synthesis: Two or more reactants combine to form a single product.
- Decomposition: A single reactant breaks down into two or more products.
- Single Displacement: One element replaces another element in a compound.
- Double Displacement: Two elements in different compounds exchange places to form new compounds.
Acid-Base Reactions
- Acid-base reactions, often called neutralization, involve the formation of water (H₂O) and a salt.
- Acids contain hydrogen (H⁺) ions. Bases contain hydroxide (OH⁻) ions.
- Acid-base reactions are double displacement.
Precipitation Reactions
- Reactions where two aqueous solutions mix, creating an insoluble solid (precipitate).
- Solubility rules are used to predict precipitates.
Redox Reactions
- Redox reactions involve electron transfer between reactants.
- One substance loses electrons (oxidation) while another gains them (reduction).
Combustion Reactions
- Combustion reactions are redox reactions where a substance reacts with oxygen to produce energy in the form of heat or light.
- When carbon and hydrogen compounds react with oxygen, they always yield carbon dioxide and water.
Predicting Products
- Use the type of reaction and reactants involved to predict the products.
- Consider solubility rules, the activity series, and the chemical nature of reactants to predict products.
Writing Equations and Predicting Products
- Use the type of reaction and the correct and/or neutral formulas for reactants and products.
- Use states of matter.
- Balance the equation using coefficients.
Predicting Products (continued)
- Determining the reaction type helps predict products.
- Consult the activity series for single-replacement reactions.
Limiting Reactions
- The limiting reactant determines the maximum amount of product.
- Determine the limiting reactant to determine how much product can be formed.
- Identify which reactant is limiting by comparing the amount of reactants available to their stoichiometric ratios, calculate how much product will be formed for each ratio.
Limiting Reactant (continued)
- Calculate the amount of product based on the complete consumption for each reactant.
- Determine which reactant is limiting using stoichiometry.
- Determine which reactant produces the smaller amount of product.
Yield
- Theoretical Yield: The maximum amount of product possible, calculated from the limiting reactant.
- Actual Yield: The amount of product experimentally obtained.
- Percent Yield: The ratio of the actual yield to the theoretical yield, expressed as a percentage.
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Description
This quiz explores the fundamentals of chemical reactions, focusing on their characteristics, evidences, and lab tests. Participants will learn about the transformation of substances, observable signs of reactions, and specific tests used in laboratory settings to identify different gases and pH levels.
