Chemical Equations and Reactions HOLT 8.1-2
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Questions and Answers

Which of the following best describes a chemical reaction?

  • The creation of new substances with different chemical and physical properties from the original substances. (correct)
  • A process where substances undergo a change in phase but their chemical composition remains the same.
  • A physical change where substances change state but retain their original chemical properties.
  • Any change to a substance that leads to an observable change in appearance.

In a chemical reaction, what are the original substances called?

  • Catalysts
  • Inhibitors
  • Products
  • Reactants (correct)

Which of the following is NOT a typical sign that a chemical reaction might be happening?

  • The production of gas, such as smoke
  • The release of energy, such as heat or light
  • A change in the color of the substance
  • The change in the shape of the substance (correct)

When wood burns in a campfire, several signs indicate a chemical reaction, which of the following is a direct indication of a chemical reaction?

<p>Ash being the end product. (A)</p> Signup and view all the answers

Based on the context, what is the main difference between a physical change and a chemical change?

<p>Physical changes alter states of matter, whereas chemical changes alter the chemical composition of the substance. (A)</p> Signup and view all the answers

Which of the following is the best way to describe the products of a chemical reaction?

<p>The substances that result from the reaction and have new physical and chemical properties. (A)</p> Signup and view all the answers

Which of these processes are primarily a result of chemical changes?

<p>Digestion and respiration. (D)</p> Signup and view all the answers

Which of the following changes best identifies a chemical reaction taking place?

<p>Milk turning sour. (C)</p> Signup and view all the answers

What does the symbol (aq) indicate in a chemical equation?

<p>A substance dissolved in water (A)</p> Signup and view all the answers

In a chemical equation, what does the symbol `` with Pd written underneath, signify?

<p>Palladium is a catalyst and it speeds up the reaction. (B)</p> Signup and view all the answers

The symbol / in a chemical equation indicates what condition?

<p>The reactants are being heated. (C)</p> Signup and view all the answers

A chemical equation shows H2O(l) H2O(g). What does this reaction represent?

<p>The boiling or vaporization of water. (A)</p> Signup and view all the answers

What does the double arrow symbol in a chemical equation indicate?

<p>The reaction is reversible and the final state consists of both product and reactant mixtures. (B)</p> Signup and view all the answers

What is the typical physical state of a substance represented by the symbol (s)?

<p>Solid (C)</p> Signup and view all the answers

Besides the symbols, what other information is typically included in most chemical reaction equations?

<p>The formulas of reactants and products (D)</p> Signup and view all the answers

Which of the following correctly describes the law of conservation of mass?

<p>Mass is neither created nor destroyed during chemical reactions. (C)</p> Signup and view all the answers

If a reaction has heat written over the reaction arrow, what is this an indication of?

<p>The reactants must be heated for the reaction to proceed. (C)</p> Signup and view all the answers

What happens to atoms during a chemical reaction?

<p>Atoms are rearranged and bonded differently. (A)</p> Signup and view all the answers

What is the purpose of balancing a chemical equation?

<p>To demonstrate the conservation of mass in chemical reactions. (D)</p> Signup and view all the answers

Why is it important to collect all products of a reaction when verifying the law of conservation of mass?

<p>To ensure that no mass is lost or gained during the reaction. (A)</p> Signup and view all the answers

In the reaction where sodium reacts with water, what are the reactants?

<p>Na and H2O (C)</p> Signup and view all the answers

What is the role of coefficients in a balanced chemical equation?

<p>Coefficients represent the number of moles of each reactant and product. (C)</p> Signup and view all the answers

In the reaction of sodium with water, which of the following represents the product(s) of the reaction?

<p>NaOH + H2 (A)</p> Signup and view all the answers

Why is the equation for the reaction of sodium with water considered unbalanced?

<p>The number of atoms of each element is not the same on both sides of the equation. (A)</p> Signup and view all the answers

What does the arrow in a chemical equation signify?

<p>Forms or produces (C)</p> Signup and view all the answers

What is the first step in writing a chemical equation?

<p>Writing a word equation (A)</p> Signup and view all the answers

In a formula equation, what do the question marks before each chemical formula indicate?

<p>That the number of molecules is unknown (C)</p> Signup and view all the answers

What does the law of conservation of mass specify with respect to chemical equations?

<p>The numbers of atoms for each element must be the same on both sides of the arrow. (A)</p> Signup and view all the answers

What is the main difference between a word equation and a formula equation?

<p>A formula equation uses chemical formulas, a word equation uses names. (A)</p> Signup and view all the answers

Which of the following is a word equation for the reaction of methane with oxygen to form carbon dioxide and water?

<p>methane + oxygen → carbon dioxide + water (B)</p> Signup and view all the answers

What does the formula CH4 represent?

<p>A molecule of methane (B)</p> Signup and view all the answers

What does the chemical equation indicate about the substances in a reaction?

<p>The amount of each particular substance (A)</p> Signup and view all the answers

What role do polyatomic ions play in balancing chemical equations?

<p>They can be counted as single units. (A)</p> Signup and view all the answers

When balancing the equation for sodium phosphate and calcium nitrate, which ions should be considered as units?

<p>Nitrate and phosphate ions. (C)</p> Signup and view all the answers

In the reaction of aluminum with sulfuric acid, how many aluminum sulfate molecules are produced?

<p>1 (B)</p> Signup and view all the answers

How many sulfate ions are present on the reactants' side in the aluminum and sulfuric acid reaction?

<p>3 (B)</p> Signup and view all the answers

What is the product formed when aluminum reacts with arsenic acid?

<p>Aluminum arsenate (B)</p> Signup and view all the answers

Why is it helpful to check the count of each atom individually after balancing an equation?

<p>To ensure the accuracy of the balance. (B)</p> Signup and view all the answers

In a balanced equation, which statement about polyatomic ions is NOT true?

<p>They must always be present in equal numbers. (C)</p> Signup and view all the answers

What is the significance of balancing chemical equations involving polyatomic ions?

<p>It allows for the preservation of mass. (C)</p> Signup and view all the answers

What is the primary goal of balancing a chemical equation?

<p>To have equal numbers of atoms for each element on both sides (D)</p> Signup and view all the answers

Which statement accurately describes coefficients in a chemical equation?

<p>They multiply the number of atoms of the substance that follows them (C)</p> Signup and view all the answers

In the unbalanced equation Na + H2O → NaOH + H2, how many hydrogen atoms are present on the reactants side?

<p>2 (A)</p> Signup and view all the answers

Which of the following is NOT a step in balancing chemical equations?

<p>Change the formulas of the reactants (C)</p> Signup and view all the answers

If a formula H2O is represented with a coefficient of 2, how many total atoms of oxygen are present?

<p>2 (A)</p> Signup and view all the answers

In balancing the equation Na + H2O → NaOH + H2, which element does NOT have an equal number of atoms on both sides?

<p>Hydrogen (C)</p> Signup and view all the answers

What does the formula 3Ca(NO3)2 signify in terms of atoms?

<p>3 calcium atoms, 6 nitrogen atoms, and 18 oxygen atoms (D)</p> Signup and view all the answers

When balancing chemical equations, what should you NOT do with the formulas of the substances involved?

<p>Change them to new formulas (A)</p> Signup and view all the answers

Flashcards

What is a chemical reaction?

A process where one or more substances change into one or more different substances with new chemical and physical properties. These substances change from reactants to products.

What are reactants?

The substances that go into a chemical reaction.

What are products?

The substances that are formed in a chemical reaction.

What is decomposition?

A chemical reaction where larger molecules are broken down into smaller ones.

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What is synthesis?

A chemical reaction where smaller molecules combine to form larger ones.

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What is a word equation?

A way to represent a chemical reaction using words.

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What is a formula equation?

A way to represent a chemical reaction using chemical formulas.

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What are notations in a formula equation?

Symbols used in formula equations that show the state of matter (solid, liquid, gas, or aqueous) of the substances involved.

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→ (yields)

Indicates that a chemical reaction has taken place, showing the transformation of reactants into products.

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←→ (reversible reaction)

Represents a reversible reaction where products can transform back into reactants, resulting in a mixture.

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∆ (heat)

Indicates that heat is applied to the reactants, speeding up the reaction.

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(s) (solid)

Substance is in the solid state, like a rock.

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(l) (liquid)

Substance is in the liquid state, like water.

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(g) (gas)

Substance is in the gaseous state, like air.

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(aq) (aqueous)

Substance is dissolved in water, forming a solution.

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Pd (catalyst)

Represents a catalyst, a substance that speeds up a reaction without being consumed.

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Chemical Equation

A symbolic representation of a chemical reaction, showing the chemical formulas of reactants and products, and their relative amounts.

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Reactants

Substances that react with each other in a chemical reaction.

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Products

Substances that are formed as a result of a chemical reaction.

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Word Equation

A representation of a chemical reaction using the names of the reactants and products.

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Formula Equation

A representation of a chemical reaction using the chemical formulas of the reactants and products.

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Balanced Chemical Equation

A chemical equation that shows the same number of atoms of each element on both sides of the equation.

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Balancing a Chemical Equation

The process of adjusting the coefficients in a chemical equation to ensure the same number of atoms of each element on both sides.

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Law of Conservation of Mass

The principle that states that in a closed system, the mass of the reactants before a chemical reaction must equal the mass of the products after the reaction.

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Coefficient

A number placed in front of a chemical formula in an equation to balance the number of atoms on each side of the equation.

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Rearrangement of atoms

In a chemical reaction, atoms are not created or destroyed, but are rearranged to form new substances.

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Reaction of sodium with water

The chemical reaction of sodium with water, where sodium atoms react with water molecules to produce sodium hydroxide and hydrogen gas.

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What is a balanced chemical equation?

A chemical equation is balanced when the number of atoms of each element on the reactants' side is equal to the number of atoms of that element on the products' side.

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What are coefficients in a chemical equation?

Coefficients are small whole numbers placed in front of chemical formulas in a chemical equation. They multiply the number of atoms of each element in the formula.

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Why can't you change the chemical formulas in a chemical equation?

You cannot change the chemical formulas of substances when balancing an equation. You can only adjust the number of molecules of each substance by changing the coefficients.

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How do you balance a chemical equation?

To balance a chemical equation, you need to find the correct coefficients that make the number of atoms of each element equal on both sides.

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What is an unbalanced chemical equation?

An unbalanced equation shows the reactants and products, but the number of atoms of each element is not equal on both sides.

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What is the first step in balancing a chemical equation?

Identify the reactants and products of the reaction. If no equation is provided, write an unbalanced equation based on the information given.

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What is the second step in balancing a chemical equation?

Count the number of atoms of each element on both sides of the unbalanced equation.

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What is the third step in balancing a chemical equation?

Adjust the coefficients in front of the formulas to make the number of atoms of each element equal on both sides.

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What are polyatomic ions?

Polyatomic ions are groups of atoms that act as a single unit in a chemical reaction. For example, the sulfate ion (SO 4 2-) is a polyatomic ion. It remains intact throughout the reaction and can be treated as a single entity when balancing the equation.

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How do you balance equations with polyatomic ions?

When balancing a chemical equation with polyatomic ions, you can treat the entire polyatomic ion as a single unit. This simplifies the process of balancing, as you focus on the ion's presence on both sides of the equation rather than individual atoms.

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Example of balancing with polyatomic ions

In the example of the reaction between aluminum and sulfuric acid, sulfate (SO 4 2-) ions are present both in the reactant (sulfuric acid) and the product (aluminum sulfate). By counting the sulfate ions as units, we observe that there are three sulfate ions on both the reactant and product sides.

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Example of balancing with polyatomic ions (sodium phosphate and calcium nitrate)

The balanced equation for the reaction of sodium phosphate (Na 3 PO 4 ) and calcium nitrate (Ca(NO 3 ) 2 ) is 2Na 3 PO 4

  • 3Ca(NO 3 ) 2 → 6NaNO 3
  • Ca 3 (PO 4 )
  1. This demonstrates how polyatomic ions are treated as units, simplifying the balancing process by focusing on the presence of entire ions instead of individual atoms.
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Verification of atom count after balancing with polyatomic ions

When balancing a chemical equation, it's crucial to check that the number of atoms of each element on the reactant side equals the number on the product side. Even after treating polyatomic ions as units, it's essential to verify the individual atom counts for accuracy.

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Study Notes

Chemical Equations and Reactions

  • Chemical reactions involve the rearrangement of atoms, not creation or destruction, this follows the law of conservation of mass.
  • Chemical reactions transform elements or compounds into new substances with different properties.
  • Reactants are the substances that undergo a change.
  • Products are the substances formed in a chemical reaction.
  • Evidence of a chemical reaction includes changes in color, formation of a precipitate (a solid), release of energy (heat or light), formation of a gas, and change in temperature.
  • A chemical equation uses chemical formulas to represent reactants and products, showing the relative amounts of each substance involved in the reaction
  • Chemical equations should always be balanced, meaning they have the same number of atoms of each element on both the reactant and product sides to maintain conservation of mass.
  • Coefficients indicate the number of molecules/formula units involved in a chemical reaction (balancing chemical equations).
  • Subscripts indicate the number of atoms of each element in a molecule (do not alter during balancing).
  • Polyatomic ions are groups of atoms that behave as units, maintaining their composition throughout the reaction. They can be treated as a single unit when balancing equations.
  • Chemical equations can include symbols that represent the physical state of reactants and products (s = solid; l = liquid; g = gas; aq = aqueous solution).
  • Physical changes do not always represent chemical reactions. These may involve changes in state (evaporation, freezing, etc.) or changes in properties without altering molecular composition.
  • The odd-even technique uses a common multiple to ensure an entire equation is balanced in certain instances.

Balancing Chemical Equations

  • The coefficients in an equation must be used correctly to balance the equation.
  • Counting the atoms of each element on both sides of the equation is crucial before balancing.
  • Balancing polyatomic ions as a unit saves time and increases accuracy in balancing complex equations.
  • Chemical reactions always follow the law of conservation of mass.
  • Using coefficients correctly to multiply the number of atoms in the formula is a critical step in balancing equations.

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Holt Chemistry Chapter 8 Chemical Equations and Reactions PDF

Description

This quiz covers the fundamentals of chemical equations and reactions. You will learn about reactants, products, and the importance of balancing equations according to the law of conservation of mass. Test your knowledge on the evidence of chemical reactions and how to represent them through chemical formulas.

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