Text A Chemistry 3.1 Chemical Reactions

Question 1

What happens when iron reacts with water and oxygen?

Answer 1

It forms rust.

This is an example of a chemical change.

Question 2

What are chemiluminescent reactions?

Answer 2

Chemical reactions in which light is given off.

This includes processes like glow sticks.

Question 3

What is bioluminescence?

Answer 3

Bioluminescence refers to light produced by living organisms.

Examples include fireflies and certain types of jellyfish.

Question 4

What is a key indicator of a chemical reaction when baking a cake?

Answer 4

The cake rises due to a chemical reaction.

This indicates the release of energy and formation of new substances.

Question 5

What is a clear evidence of a chemical reaction?

Answer 5

Release or absorption of energy.

This can manifest as temperature changes, light, or sound.

Question 6

What are the reactants in the reaction of carbon and oxygen forming carbon dioxide?

Answer 6

Carbon (C) and oxygen (O₂).

Carbon dioxide (CO₂) is the product.

Question 7

What are the products in the reaction of carbon and oxygen forming carbon dioxide?

Answer 7

Carbon dioxide (CO₂).

The reactants are carbon and oxygen.

Question 8

List the types of evidence of chemical reactions.

Answer 8

• Energy change
• Odour change
• Colour change
• Formation of a gas
• Formation of a solid (precipitate) in solution

These indicators help identify chemical changes.

Question 9

What can indicate a change in energy during a chemical reaction?

Answer 9

Temperature change, emission of light, emission of sound, or electrical energy.

These observations help determine the nature of the chemical reaction.

Question 10

True or False: All chemical reactions involve a change in energy.

Answer 10

True.

Energy changes are a fundamental aspect of chemical reactions.

Question 11

Fill in the blank: A chemical reaction occurs when one or more substances change to form _______.

Answer 11

[different substances].

This distinguishes chemical reactions from physical changes.

Question 12

What happens to the odour of products compared to reactants in some chemical reactions?

Answer 12

The odour of the products may differ from that of the reactants.

This change can indicate a chemical reaction has occurred.

Question 13

What can indicate the formation of gas in a chemical reaction?

Answer 13

Bubbles in the solution.

This is a common observation in reactions occurring in liquid.

Question 14

What occurs when a substance that is not soluble is formed in a solution?

Answer 14

It comes out of solution as a solid (precipitate).

This is another indication of a chemical reaction.

Question 15

What compounds react in highway flares?

Answer 15

Potassium perchlorate, sulfur, and other compounds

These compounds release energy as light and thermal energy.

Question 16

What is the reaction of substances in bleach with colored compounds?

Answer 16

They form colorless compounds

This reaction is useful for removing stains from white fabric.

Question 17

What happens when baking powder reacts in batter at high temperatures?

Answer 17

Bubbles of gas form, causing the batter to rise

This is why batter rises when placed in the oven.

Question 18

What does the combustion of fuel such as gasoline produce?

Answer 18

Energy in the form of heat and gases

The expanding gases drive the pistons in the engine of the car.

Question 19

What causes the characteristic smell of lightning storms?

Answer 19

Ozone and other substances formed by chemical reactions from electrical energy of lightning

These substances contribute to the distinctive odor.

Question 20

What is a precipitate?

Answer 20

An insoluble solid formed in a chemical reaction that occurs in solution

Such reactions often involve ionic compounds.

Question 21

What happens to ionic compounds when they dissolve in water?

Answer 21

The ions break away from the crystal lattice structure and move freely in the water

Many ionic compounds are soluble in water.

Question 22

What indicates that a chemical reaction has taken place when mixing ionic compounds?

Answer 22

The formation of a precipitate

The solution turns cloudy, and particles may collect at the surface or bottom.

Question 23

What occurs when hard water contains dissolved ions that react with soap?

Answer 23

Insoluble compounds form as products, appearing as a precipitate called soap scum

This is an example of precipitation.

Question 24

What changes occur to food when it is cooked?

Answer 24

The odor, color, and taste of food change due to chemical reactions

These reactions alter the substances in the food.

Question 25

Fill in the blank: The process that produces energy in the form of heat and gases from fuel is called _______.

Answer 25

combustion

Question 26

True or False: All ionic compounds dissolve well in water.

Answer 26

False ## Footnote Some ionic compounds do not dissolve well in water.

Question 27

What visual change indicates the formation of a precipitate?

Answer 27

The solution turns cloudy ## Footnote Particles of the precipitate may collect at the surface or bottom.

Question 28

What is the white precipitate formed when silver nitrate solution is added to a solution containing dissolved sodium chloride?

Answer 28

Silver chloride (AgCl) ## Footnote The formation of AgCl is indicated by the white precipitate in the reaction between AgNO3 and NaCl.

Question 29

How can you predict if a certain pair of positive and negative ions will combine to form a precipitate in an aqueous solution?

Answer 29

By testing a wide range of ionic compounds for solubility in water ## Footnote This involves using solubility tables that outline the solubility of various ionic compounds.

Question 30

What does Table 3.2 outline regarding ionic compounds?

Answer 30

The solubility of ionic compounds in water at 25°C ## Footnote It categorizes ionic compounds based on their solubility as either high or low.

Question 31

What ions are categorized under high solubility in Table 3.2?

Answer 31

* NH4+ * NO3- * ClO3- * ClO4- * CH3COO- * Group 1 ions ## Footnote These ions are generally soluble in water.

Question 32

What ions are categorized under low solubility in Table 3.2?

Answer 32

* Ag+ * Hg2+ * Pb2+ * Ca2+ * Ba2+ * Sr2+ * Ra2+ * S2- * OH- ## Footnote These ions often form precipitates in aqueous solutions.

Question 33

How can you determine the solubility of barium hydroxide, Ba(OH)2, in water?

Answer 33

Locate Ba2+ or OH- in Table 3.2 and check their solubility category ## Footnote Ba(OH)2 is soluble because Ba2+ is listed under 'High solubility.'

Question 34

What is the solubility of silver sulfide, Ag2S, in water?

Answer 34

Relatively low solubility ## Footnote The sulfide ion is categorized under low solubility, indicating Ag2S does not dissolve well in water.

Question 35

What inference can a chemist make if a white precipitate forms upon adding silver nitrate solution to a solution being tested?

Answer 35

There are likely chloride ions (Cl-) in the solution ## Footnote The formation of the precipitate indicates the presence of Cl- ions.

Question 36

What is a useful method for predicting whether a precipitate will form when mixing two solutions?

Answer 36

Drawing diagrams to visualize the mixing process ## Footnote This helps in understanding the interactions between ions in the solutions.

Question 37

Fill in the blank: The negative ion, OH-, is in the _______ of Table 3.2.

Answer 37

seventh column ## Footnote The position of OH- helps determine its solubility with various cations.

Question 38

What process do plants use to absorb carbon dioxide and produce oxygen?

Answer 38

Photosynthesis ## Footnote Photosynthesis is an endothermic process that requires energy from the Sun.

Question 39

What is the reverse process of photosynthesis?

Answer 39

Cellular respiration ## Footnote Cellular respiration converts glucose and oxygen into carbon dioxide and water, releasing energy.

Question 40

What do organisms use energy from cellular respiration for?

Answer 40

To carry out every function ## Footnote Functions include running, solving problems, breathing, and digesting food.

Question 41

What do all chemical reactions do in terms of energy?

Answer 41

Release or absorb energy ## Footnote This is a fundamental characteristic of chemical reactions.

Question 42

What is required for photosynthesis to proceed?

Answer 42

Energy from the Sun ## Footnote Photosynthesis converts carbon dioxide and water to glucose and oxygen.

Question 43

What evidence suggests that photosynthesis requires light energy?

Answer 43

Plants do not produce oxygen at night ## Footnote A plant kept in darkness will eventually die due to lack of food production.

Question 44

What are reactions that release energy called?

Answer 44

Exothermic reactions ## Footnote Examples include cellular respiration, explosions, combustion, and rusting.

Question 45

What is an example of an exothermic reaction?

Answer 45

Combustion of gasoline ## Footnote Other examples include cellular respiration and explosions.

Question 46

What type of reactions require continuous addition of energy?

Answer 46

Endothermic reactions ## Footnote Cooking food is an example where energy is absorbed by the reactants.

Question 47

Fill in the blank: Reactions that absorb energy are called _______.

Answer 47

Endothermic reactions ## Footnote These reactions require energy input to proceed.

Question 48

What does the law of conservation of energy state?

Answer 48

Energy can be converted from one form to another, but the total energy of the universe remains constant.

Question 49

Who are the scientists credited with developing the law of conservation of energy?

Answer 49

Hermann Helmholtz, James Joule, and Julius Robert Mayer.

Question 50

What is a common misconception about burning wood in relation to energy conservation?

Answer 50

It may seem that energy is created, but energy is conserved overall.

Question 51

What is chemical energy?

Answer 51

The energy present in the bonds of the reactants and products of every chemical reaction.

Question 52

What happens to chemical bonds during a chemical reaction?

Answer 52

Bonds in the reactants break and new bonds form in the products.

Question 53

What type of process is breaking chemical bonds?

Answer 53

Endothermic process.

Question 54

What type of process is forming new chemical bonds?

Answer 54

Exothermic process.

Question 55

How is the energy change in a chemical reaction determined?

Answer 55

It is equal to the difference between the energy required to break bonds and the energy released when bonds are formed.

Question 56

What characterizes an endothermic reaction?

Answer 56

More energy is required to break bonds than is released when new bonds form.

Question 57

What characterizes an exothermic reaction?

Answer 57

Less energy is required to break bonds than is released when new bonds form.

Question 58

Fill in the blank: The electrolysis of water to form hydrogen and oxygen is an _______ reaction.

Answer 58

endothermic

Question 59

Fill in the blank: When hydrogen and oxygen react to form water, energy is _______.

Answer 59

released

Question 60

What is an example of an exothermic reaction?

Answer 60

The reaction of hydrogen and oxygen to form water.

Question 61

What does a change in energy indicate?

Answer 61

It does not always mean a chemical change has taken place; physical changes can also involve energy changes.

Question 62

List three examples of physical changes and classify them as endothermic or exothermic.

Answer 62

* Melting ice - endothermic * Freezing water - exothermic * Evaporating water - endothermic

Question 63

What questions would you ask to determine whether a change is physical or chemical?

Answer 63

Consider whether new substances are formed or if the change can be reversed.