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Questions and Answers
In a chemical equation, what information is conveyed by the arrow symbol?
In a chemical equation, what information is conveyed by the arrow symbol?
- Indicates the presence of a catalyst.
- Represents 'yields' or 'reacts to produce'. (correct)
- Denotes the state of matter of a substance.
- Shows the reaction is reversible.
What is the primary difference between a word equation and a skeleton equation?
What is the primary difference between a word equation and a skeleton equation?
- A word equation represents reversible reactions; a skeleton equation, irreversible ones.
- A word equation is always balanced, while a skeleton equation is not.
- A word equation includes the states of matter, while a skeleton equation does not.
- A word equation uses chemical names, while a skeleton equation uses chemical symbols. (correct)
Which of the following is true regarding skeleton equations?
Which of the following is true regarding skeleton equations?
- They must always be balanced to adhere to the law of conservation of mass.
- They show the formulas of reactants and products without indicating their relative quantities. (correct)
- They use words to represent reactants and products.
- They indicate the relative amounts of reactants and products.
In a balanced chemical equation, what role do coefficients play?
In a balanced chemical equation, what role do coefficients play?
Which states of matter are commonly indicated in chemical equations using abbreviations?
Which states of matter are commonly indicated in chemical equations using abbreviations?
In a chemical equation, what does the symbol $\Delta$ (or 'heat') above the arrow signify?
In a chemical equation, what does the symbol $\Delta$ (or 'heat') above the arrow signify?
What is the role of a catalyst in a chemical reaction, and how is its presence indicated in a chemical equation?
What is the role of a catalyst in a chemical reaction, and how is its presence indicated in a chemical equation?
Which type of chemical reaction involves a single compound breaking down into two or more products?
Which type of chemical reaction involves a single compound breaking down into two or more products?
What is a key characteristic of a single-replacement reaction?
What is a key characteristic of a single-replacement reaction?
In a double-replacement reaction, what typically drives the reaction to completion?
In a double-replacement reaction, what typically drives the reaction to completion?
What is always required for a chemical reaction to be classified as a combustion reaction?
What is always required for a chemical reaction to be classified as a combustion reaction?
Which of the following best describes a synthesis reaction?
Which of the following best describes a synthesis reaction?
In the context of stoichiometry, what does the 'law of conservation of mass' imply for balanced chemical equations?
In the context of stoichiometry, what does the 'law of conservation of mass' imply for balanced chemical equations?
What is defined as a conversion factor derived from the coefficients of a balanced chemical reaction interpreted in terms of moles?
What is defined as a conversion factor derived from the coefficients of a balanced chemical reaction interpreted in terms of moles?
If you are given the mass of a reactant and asked to find the mass of a product, what is the correct sequence of steps using stoichiometry?
If you are given the mass of a reactant and asked to find the mass of a product, what is the correct sequence of steps using stoichiometry?
Consider the reaction: $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$. If you start with 4 moles of $H_2$, how many moles of $O_2$ are required for complete reaction?
Consider the reaction: $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$. If you start with 4 moles of $H_2$, how many moles of $O_2$ are required for complete reaction?
What is the limiting reagent in a chemical reaction?
What is the limiting reagent in a chemical reaction?
In a chemical reaction, what term describes the reactant that remains after the limiting reactant is completely consumed?
In a chemical reaction, what term describes the reactant that remains after the limiting reactant is completely consumed?
Consider the reaction: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$. If you start with 2 moles of $N_2$ and 5 moles of $H_2$, which is the limiting reagent?
Consider the reaction: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$. If you start with 2 moles of $N_2$ and 5 moles of $H_2$, which is the limiting reagent?
What is the first step in determining the limiting reagent when given the mass of each reactant?
What is the first step in determining the limiting reagent when given the mass of each reactant?
The theoretical yield of a reaction represents:
The theoretical yield of a reaction represents:
What is the definition of 'actual yield' in a chemical reaction?
What is the definition of 'actual yield' in a chemical reaction?
What does percent yield measure in a chemical reaction?
What does percent yield measure in a chemical reaction?
How is percent yield calculated?
How is percent yield calculated?
What is a key assumption when determining theoretical yield in a chemical reaction?
What is a key assumption when determining theoretical yield in a chemical reaction?
Consider a chemical reaction where the theoretical yield is 50.0 grams, but the actual yield is 45.0 grams. What is the percent yield?
Consider a chemical reaction where the theoretical yield is 50.0 grams, but the actual yield is 45.0 grams. What is the percent yield?
Which factor can cause the actual yield of a reaction to be less than the theoretical yield?
Which factor can cause the actual yield of a reaction to be less than the theoretical yield?
What is the mole ratio of $N_2$ to $NH_3$ in the balanced equation $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$?
What is the mole ratio of $N_2$ to $NH_3$ in the balanced equation $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$?
How many moles of oxygen are required to completely react with 1 mole of methane ($CH_4$) in the combustion reaction: $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$?
How many moles of oxygen are required to completely react with 1 mole of methane ($CH_4$) in the combustion reaction: $CH_4(g) + 2O_2(g) \rightarrow CO_2(g) + 2H_2O(g)$?
If 10.0 g of $H_2$ reacts with excess $N_2$, how many grams of $NH_3$ can be produced according to the reaction: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$? (Molar mass of $H_2$ = 2.0 g/mol, Molar mass of $NH_3$ = 17.0 g/mol)
If 10.0 g of $H_2$ reacts with excess $N_2$, how many grams of $NH_3$ can be produced according to the reaction: $N_2(g) + 3H_2(g) \rightarrow 2NH_3(g)$? (Molar mass of $H_2$ = 2.0 g/mol, Molar mass of $NH_3$ = 17.0 g/mol)
In the reaction: $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$, if 48.6 g of Mg reacts with 32.0 g of $O_2$, what mass of MgO will be produced? (Molar mass of Mg = 24.3 g/mol, Molar mass of $O_2$ = 32.0 g/mol, Molar mass of MgO = 40.3 g/mol)
In the reaction: $2Mg(s) + O_2(g) \rightarrow 2MgO(s)$, if 48.6 g of Mg reacts with 32.0 g of $O_2$, what mass of MgO will be produced? (Molar mass of Mg = 24.3 g/mol, Molar mass of $O_2$ = 32.0 g/mol, Molar mass of MgO = 40.3 g/mol)
For the reaction: $C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)$, if 44.0 g of $C_3H_8$ is reacted with excess $O_2$ and 88.0 g of $CO_2$ is collected, what is the percent yield of $CO_2$? (Molar mass of $C_3H_8$ is 44.0 g/mol, Molar mass of $CO_2$ is 44.0 g/mol)
For the reaction: $C_3H_8(g) + 5O_2(g) \rightarrow 3CO_2(g) + 4H_2O(g)$, if 44.0 g of $C_3H_8$ is reacted with excess $O_2$ and 88.0 g of $CO_2$ is collected, what is the percent yield of $CO_2$? (Molar mass of $C_3H_8$ is 44.0 g/mol, Molar mass of $CO_2$ is 44.0 g/mol)
What is the mole ratio of $H_2O$ to $O_2$ in the reaction $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$?
What is the mole ratio of $H_2O$ to $O_2$ in the reaction $2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$?
What is stoichiometry primarily used for?
What is stoichiometry primarily used for?
In the context of chemical reactions, what does the term 'limiting ingredient' refer to?
In the context of chemical reactions, what does the term 'limiting ingredient' refer to?
Consider the reaction: $2 Cu(s) + S(s) \rightarrow Cu_2S(s)$. If you have 127 g of copper (Cu) and 32 g of sulfur (S), which is the limiting reagent? (Molar mass of Cu = 63.5 g/mol, Molar mass of S = 32 g/mol)
Consider the reaction: $2 Cu(s) + S(s) \rightarrow Cu_2S(s)$. If you have 127 g of copper (Cu) and 32 g of sulfur (S), which is the limiting reagent? (Molar mass of Cu = 63.5 g/mol, Molar mass of S = 32 g/mol)
Flashcards
What are Reactants?
What are Reactants?
Substances present before a chemical reaction, written on the left side of the reaction arrow.
What are Products?
What are Products?
Substances present after a chemical reaction, written on the right side of the reaction arrow.
What is a Word Equation?
What is a Word Equation?
Uses full names of elements/compounds to describe reactants and products.
What is a Skeleton Equation?
What is a Skeleton Equation?
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What is Material State?
What is Material State?
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What is a Decomposition Reaction?
What is a Decomposition Reaction?
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What is the Law of Conservation of Mass?
What is the Law of Conservation of Mass?
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What are Coefficients?
What are Coefficients?
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What is a Combination (Synthesis) Reaction?
What is a Combination (Synthesis) Reaction?
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What is a Single-Replacement Reaction?
What is a Single-Replacement Reaction?
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What is a Double-Replacement Reaction?
What is a Double-Replacement Reaction?
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What is a Combustion Reaction?
What is a Combustion Reaction?
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What is Stoichiometry?
What is Stoichiometry?
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What is a Mole Ratio?
What is a Mole Ratio?
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What is the Limiting Reagent?
What is the Limiting Reagent?
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What is the Excess Reagent?
What is the Excess Reagent?
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What is Theoretical Yield?
What is Theoretical Yield?
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What is Actual Yield?
What is Actual Yield?
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What is Percent Yield?
What is Percent Yield?
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Study Notes
Chemical Equations
- Chemical reactions involve one or more substances changing into different substances.
- Representing a chemical reaction involves indicating substances before (reactants) and after (products) the reaction arrow.
- Word equations are descriptions using words, quicker to write and easier to interpret than sentences.
- For example, iron and oxygen yield iron(III) oxide (rust).
Chemical Equations & Symbols
- Skeleton equations use chemical symbols instead of words.
- Skeleton equations show the formulas of reactants and products, but do not indicate relative amounts.
- Word equations use full names of elements and compounds to describe reactants and products.
- Reactants are on the left side of the arrow, and the products are on the right side.
- Reactants and products can be represented by:
- Solids (s)
- Gases (g)
- Liquids (l)
- Aqueous solutions (aq)
- "+" separates reactants or products.
- "→" means "yields," separating reactants from products.
Chemical Reactions
- "⇌" indicates a reversible reaction.
- The state of a substance follows its formula e.g., (s), (l), (g).
- (aq) indicates an aqueous solution, substance dissolved in water.
- "Δ" or "heat" indicates heat is supplied to start a reaction.
- A formula above or below "→" indicates a catalyst, like platinum (Pt;), which speeds up the reaction.
Balancing Equations
- Conservation of mass states matter is conserved so the mass of products equals the mass of reactants in reactions
- Atoms rearrange, but remain the same type and number.
- Skeleton equations do not indicate the quantity of reactants to make a product
- Balanced equations requires the same number of components on both sides.
- Coefficients are numbers in front of terms added to balance equations.
Balancing Chemical Equations
- To balance an equation:
- First write the skeleton equation.
- Use coefficients to balance to obey the law of conservation of mass.
- Coefficients are numbers in front of terms to balance the equation.
- Balanced skeleton equations has the same number of atoms on each side
Types of Chemical Reactions
- Combination (synthesis): Two substances combine into one.
- Decomposition: One substance breaks into two.
- Single-replacement: One element replaces another in a compound.
- Double-replacement: Two compounds exchange positive ions.
Combination, Combustion & Decomposition Reactions
- Combination reactions yields a chemical change where two or more substances form a single new substance; also called synthesis reactions (often exothermic)
- Reactions between alkali metals and halogens form binary ionic compounds (e.g., KCl, NaCl).
- Two nonmetals, sulfur and oxygen, can form multiple products in combination reactions.
- Magnesium combines with oxygen to form magnesium oxide when magnesium ribbon is ignited.
- Combustion always involves oxygen and is exothermic.
- It often involves a hydrocarbon.
- Decomposition yields a chemical change where a single compound breaks into two or more products (can be any combination of elements and compounds)
- Predicting products is difficult.
Single & Double Replacement Reactions
- Single-replacement reactions has one element replaces a second element in a compound
- Both reactants and products consist of an element and a compound.
- A double-replacement reaction has positive ions exchanged between two compounds.
- They occur in ionic aqueous solutions
- Often they form a gas, a molecular compound (e.g., water), or a precipitate.
- Precipitation reactions form an insoluble ionic compound (precipitate).
Combustion Reactions
- In combustion, a chemical change happens when an element or compound reacts with oxygen, creating energy as heat and light.
- Oxygen always is a reactant.
- Often the other reactant is a hydrocarbon.
Predicting Reaction Products
- After learning the basic chemical reactions, products of many reactions can be predicted.
- Determine the probable reaction type by examining the number and form of reactants.
- General equations serve as representations.
- Combination (Synthesis) - 2Mg(s) + O2(g) -> 2MgO(s)
- Decomposition - 2HgO(s) -> 2Hg(l) + O2(g)
- Single-Replacement - A + BC -> AC + B
- Double-Replacement - AB + CD -> AD + CB
Balancing Chemical Equations & Recipes
- Combustion involves oxygen and a compound C, H, and O.
- The products are CO2 and H2O, or C and CO.
- Balanced equations can be used as recipes, they provide the ingredients that are needed and their proper ratios:
- Equipment needed to make tricycles requires quantitative information
- Ratios of reactants to products can be used as a conversion factor to determine the number of parts needed
Interpreting Chemical Equations
- Quantifying reactants and products involves moles, mass, volume, and the number of molecules, which relates to stoichiometry:
- balanced chemical equations give relative amounts of reactants and products.
- Mass is neither created nor destroyed (law of conservation of mass).
- Atoms rearrange to form new molecules, however the number of atoms and the total mass of reactants and products remains the same
- Chemical equations are like recipes as they describe the ingredients that are needed and their proper ratios
Chemical Reactions
- Proportionality exists between reactants and products.
- In chemical equations:
- Chemical symbols provide the ingredients.
- Coefficients provide the proper ratios.
- Stoichiometry calculates the moles, mass, volume, or number of atoms or molecules of products or reactants by using balanced chemical equations.
- Mole ratio of nitrogen to ammonia is shown using the slope of a graph that shows the coefficients in the chemical equation.
Stoichiometric Calculations & Moles
- A mole is a unit for measuring the amount of a substance.
- It contains 6.02 x 1023 representative particles
- A mole ratio is is a conversion factor derived from the coefficients of a (mole ratio) from a balanced chemical equation that is used to convert between different reactants or products.
- A graph using the coefficients in the chemical equation provides proportionality between individual reactants.
Mole Ratios
- Multiplying the given number of moles by the appropriates mole ratio gives the moles of the wanted quantity.
- Mole ratios can be used in mass-mass calculations, a conversion between the mass of one reactant or produce to the mass of another.
Limiting Reagent & Equations
- The amount of any ingredient will limit the amount of product that one can make
- The limiting ingredients determines the amount of product you can make
Excess & Limiting Reagents
- Insufficient quantities of any reactant limits the amount of product formed
- The limiting reagent determines how much product is formed.
- The reaction stops when the limiting reagent is used up.
- Excess reagent is any reactant not completely used up.
- In stoichiometric problems that are often given quantities are not shown in moles.
Mass from Limiting Reagents
- To determine mass use the mole ratio to determine the number of moles one of of hte reactants to complete the reaction
- Compare mass of reactants to determine a limiting reatant from the mole ration
- The limiting reagent limits the reaction, this is used in the mole-mass reaction with mole ration to determine product
Actual & Theoretical Yield
- Using a balanced chemical equation will determine the theoretical yield.
- Actual means, the actual mass that was produced during the experiment
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