Text A Chemistry : 3.2 Representing Chemical Reactions

Question 1

What did Lavoisier observe when carrying out reactions in closed systems?

Answer 1

The system did not gain or lose mass

This observation led to the formulation of the law of conservation of mass.

Question 2

What is the law of conservation of mass?

Answer 2

During a chemical reaction, the total mass of the reactants is equal to the total mass of the products

This law was first developed by Antoine Lavoisier.

Question 3

What symbols do scientists use to represent elements?

Answer 3

Chemical symbols, such as H for hydrogen and O for oxygen

Chemical symbols are a shorthand for representing elements in chemical reactions.

Question 4

How is a chemical reaction represented?

Answer 4

Using a combination of chemical formulas and symbols

For example, the reaction of hydrogen and oxygen to form water is represented as 2H₂(g) + O₂(g) → 2H₂O.

Question 5

What is a closed system in the context of chemical reactions?

Answer 5

A system that does not allow any exchange of matter between the system and its surroundings

An example is a tightly capped test tube containing a solution.

Question 6

What is an open system in the context of chemical reactions?

Answer 6

A system that allows the exchange of substances between the system and its surroundings

An example is an open test tube containing a solution.

Question 7

What was one of Lavoisier’s significant techniques as a scientist?

Answer 7

Careful measurement of mass

This technique was crucial for making accurate inferences about chemical changes.

Question 8

What did Lavoisier stress the importance of in chemical reactions?

Answer 8

Measuring the mass of all substances involved

Accurate measurements were essential for establishing the law of conservation of mass.

Question 9

Fill in the blank: The equation for the reaction of hydrogen with oxygen to form water is _______.

Answer 9

2H₂(g) + O₂(g) → 2H₂O

Question 10

True or False: A chemical system includes all substances involved in a reaction and the container that holds them.

Answer 10

True

This definition helps to clarify what constitutes a chemical system.

Question 11

What did Lavoisier generalize from many observations?

Answer 11

His version of the law of conservation of mass

This generalization was based on careful measurements and consistent results.

Question 12

What did Lavoisier observe when carrying out reactions in closed systems?

Answer 12

The system did not gain or lose mass

This observation led to the formulation of the law of conservation of mass.

Question 13

What is the law of conservation of mass?

Answer 13

During a chemical reaction, the total mass of the reactants is equal to the total mass of the products

This law was first developed by Antoine Lavoisier.

Question 14

What symbols do scientists use to represent elements?

Answer 14

Chemical symbols, such as H for hydrogen and O for oxygen

Chemical symbols are a shorthand for representing elements in chemical reactions.

Question 15

How is a chemical reaction represented?

Answer 15

Using a combination of chemical formulas and symbols

For example, the reaction of hydrogen and oxygen to form water is represented as 2H₂(g) + O₂(g) → 2H₂O.

Question 16

What is a closed system in the context of chemical reactions?

Answer 16

A system that does not allow any exchange of matter between the system and its surroundings

An example is a tightly capped test tube containing a solution.

Question 17

What is an open system in the context of chemical reactions?

Answer 17

A system that allows the exchange of substances between the system and its surroundings

An example is an open test tube containing a solution.

Question 18

What was one of Lavoisier’s significant techniques as a scientist?

Answer 18

Careful measurement of mass

This technique was crucial for making accurate inferences about chemical changes.

Question 19

What did Lavoisier stress the importance of in chemical reactions?

Answer 19

Measuring the mass of all substances involved

Accurate measurements were essential for establishing the law of conservation of mass.

Question 20

Fill in the blank: The equation for the reaction of hydrogen with oxygen to form water is _______.

Answer 20

2H₂(g) + O₂(g) → 2H₂O

Question 21

True or False: A chemical system includes all substances involved in a reaction and the container that holds them.

Answer 21

True

This definition helps to clarify what constitutes a chemical system.

Question 22

What did Lavoisier generalize from many observations?

Answer 22

His version of the law of conservation of mass

This generalization was based on careful measurements and consistent results.

Question 23

What is the simplest form of a chemical equation?

Answer 23

Word equation

A word equation shows reactants and products using their names.

Question 24

In a word equation, what does the plus sign represent?

Answer 24

Means ‘reacts with’

It indicates the reactants in a chemical reaction.

Question 25

What does the arrow in a chemical equation signify?

Answer 25

Means 'produces' ## Footnote It separates reactants from products.

Question 26

What is a skeleton equation?

Answer 26

A bare-bones representation of a word equation ## Footnote It uses chemical symbols and formulas but is not complete.

Question 27

What does a skeleton equation fail to show?

Answer 27

Conservation of mass ## Footnote It does not accurately represent the number of atoms or molecules.

Question 28

What does Lavoisier's law of conservation of mass state?

Answer 28

Reactants have the same total mass as products ## Footnote It is fundamental to balancing chemical equations.

Question 29

What is the significance of balancing a chemical equation?

Answer 29

Shows that atoms are conserved in a chemical reaction ## Footnote Balancing reflects the principle that atoms are not created or destroyed.

Question 30

In the equation H2 + O2 → 2H2O, how many hydrogen atoms are present on each side?

Answer 30

Two hydrogen atoms ## Footnote This shows that hydrogen is balanced in the equation.

Question 31

In the same equation, how many oxygen atoms are on the left side?

Answer 31

Two oxygen atoms ## Footnote There is only one oxygen atom on the right side, making it unbalanced.

Question 32

What are coefficients in a chemical equation?

Answer 32

Numbers added before chemical formulas ## Footnote They indicate the number of molecules or atoms involved.

Question 33

What happens when you add the coefficient 2 in front of H2O?

Answer 33

Indicates two molecules of water ## Footnote It affects the total number of hydrogen and oxygen atoms.

Question 34

Why does adding the coefficient 2 in front of H2O not balance the equation?

Answer 34

It results in four hydrogen atoms on the right ## Footnote This exceeds the two hydrogen atoms on the left.

Question 35

Fill in the blank: Some elements exist as _______ rather than single atoms.

Answer 35

molecules ## Footnote For example, oxygen exists as O2, not O.

Question 36

Translate the word equation 'chlorine + sodium iodide → iodine sodium chloride' into a skeleton equation.

Answer 36

Cl2 + NaI → I2 + NaCl ## Footnote This represents the reactants and products using chemical symbols.

Question 37

What is the balanced chemical equation for the formation of water at room temperature?

Answer 37

2H2(g) + O2(g) → 2H2O ## Footnote The equation includes the physical states of the reactants and product.

Question 38

What does the abbreviation (aq) stand for in a chemical equation?

Answer 38

aqueous solution (dissolved in water) ## Footnote This indicates that the substance is dissolved in water.

Question 39

What is the difference between an endothermic and exothermic reaction?

Answer 39

In an endothermic reaction, energy is a reactant; in an exothermic reaction, energy is a product. ## Footnote Examples include the decomposition of copper(II) oxide (endothermic) and the reaction of sulfuric acid with sodium hydroxide (exothermic).

Question 40

What is the skeleton equation?

Answer 40

A representation of a chemical reaction showing the reactants and products with their correct formulas. ## Footnote Each reactant and product constitutes a 'term' in the equation.

Question 41

What is the first step in balancing a chemical equation?

Answer 41

Write the skeleton equation with correct formulas for all compounds and elements. ## Footnote This ensures that all reactants and products are correctly identified before balancing.

Question 42

What should you do when you identify an unbalanced atom or polyatomic ion?

Answer 42

Write coefficients to balance them. ## Footnote Focus on unbalanced elements that appear just once on each side of the equation.

Question 43

How do you handle fractional coefficients when balancing a chemical equation?

Answer 43

Clear any fractional coefficients by multiplying the whole equation by the same factor. ## Footnote This results in the smallest possible whole number coefficients.

Question 44

True or False: The coefficient '1' is included in a balanced chemical equation.

Answer 44

False ## Footnote Coefficient '1' is typically omitted in chemical equations.

Question 45

What is an example of an endothermic reaction?

Answer 45

CuO + thermal energy → Cu + O2(g) ## Footnote This reaction shows the decomposition of copper(II) oxide requiring thermal energy.

Question 46

What is an example of an exothermic reaction?

Answer 46

H2SO4(aq) + 2NaOH(aq) → 2H2O + Na2SO4(aq) + thermal energy ## Footnote This reaction produces water and sodium sulfate while releasing thermal energy.

Question 47

How can you verify that a chemical equation is balanced?

Answer 47

Make a table of the atoms of each element on each side of the equation. ## Footnote This helps ensure that the number of each type of atom is the same on both sides.