Topic 3: Chemical Reactions Flashcards
1
Q
What is the purpose of chemical reactions?
A
To help elements achieve a more stable energy state by gaining a full outer shell of electrons.
2
Q
What happens to bonds during a chemical reaction?
A
Old bonds are broken, and new bonds are formed, involving energy transfer.
3
Q
What is the system in a chemical reaction?
A
The actual chemicals and their bonding.
4
Q
What are the surroundings in a chemical reaction?
A
Everything outside the chemical system, such as the air, beaker, or thermometer.
5
Q
What form of energy is usually transferred in chemical reactions?
A
Heat energy, although sometimes light or sound energy is also produced.
6
Q
What is an exothermic reaction?
A
A reaction that releases heat energy to the surroundings, increasing the temperature.
7
Q
How does an exothermic reaction affect the energy of the system?
A
The energy of the system decreases as energy is transferred to the surroundings.
8
Q
What are some examples of exothermic reactions?
A
Combustion (burning fuels releases heat), oxidation (like rusting, which releases heat slowly), and neutralization reactions (when acids and bases react, releasing heat).
9
Q
Why are hand warmers considered exothermic?
A
They release heat from an exothermic reaction to warm the hands.
10
Q
How do self-heating cans work?
A
They contain an exothermic reaction in the base that releases heat to warm food or drinks.
11
Q
What is an endothermic reaction?
A
A reaction that absorbs heat energy from the surroundings, decreasing the temperature.
12
Q
How does an endothermic reaction affect the energy of the system?
A
The energy of the system increases as it absorbs energy from the surroundings.
13
Q
What are some examples of endothermic reactions?
A
Electrolysis, thermal decomposition, and the first stages of photosynthesis.
14
Q
Why are sports injury cold packs endothermic?
A
They absorb heat from the injured area, reducing swelling.
15
Q
What does energy conservation in reactions mean?
A
According to the Law of Conservation of Energy, energy cannot be created or destroyed, only transferred between the system and surroundings or converted to different forms.
16
Q
What does a thermometer measure in a reaction?
A
A thermometer measures the temperature change in the surroundings, which indicates whether heat is being released to or absorbed from the surroundings.
17
Q
What is activation energy?
A
The minimum amount of energy required for a reaction to occur.
18
Q
Why do some reactions require activation energy?
A
Because chemical bonds in reactant molecules must be broken before new bonds can form.
19
Q
Do all reactions have activation energy?
A
Yes, all reactions require some energy input to start breaking bonds.
20
Q
What happens to the activation energy in spontaneous reactions?
A
Spontaneous reactions have relatively low activation energy barriers, allowing them to occur without significant energy input from external sources.
21
Q
What is a reaction profile?
A
A graphical representation of the energy changes in a chemical reaction.
22
Q
What does a reaction profile show?
A
The energy levels of reactants and products and the activation energy required.
23
Q
What does a downward arrow in a reaction profile indicate?
A
An exothermic reaction, where energy is released.
24
Q
What does an upward arrow in a reaction profile indicate?
A
An endothermic reaction, where energy is absorbed.
25
What determines if a reaction is overall endothermic or exothermic?
The overall energy change depends on whether more energy is absorbed during bond breaking than is released during bond formation, or vice versa.
26
What happens in bond breaking?
Energy is absorbed, making it an endothermic process.
27
What happens in bond forming?
Energy is released, making it an exothermic process.
28
When is a reaction overall exothermic?
When more energy is released from forming bonds than is absorbed from breaking bonds.
29
When is a reaction overall endothermic?
When more energy is absorbed to break bonds than is released from forming bonds.
30
What is the energy change equation?
Energy change = Energy absorbed in bond breaking - Energy released in bond formation.
31
What is a bond energy?
The amount of energy required to break a bond or released when a bond is formed.
32
How can bond energies be used to determine if a reaction is exothermic or endothermic?
By comparing the total energy needed to break bonds with the total energy released in bond formation.
33
What does a positive energy change mean?
The reaction is endothermic, meaning the products have more energy than the reactants.
34
What does a negative energy change mean?
The reaction is exothermic, meaning the products have less energy than the reactants.
35
Why is it helpful to write displayed formula equations for bond energy calculations?
It helps to identify the type and number of bonds accurately, reducing mistakes.
36
Why is it important to remember bond breaking is endothermic?
Because it requires energy input, leading to the end of that bond.
37
Why do reactions with high activation energy require heat?
Because more energy is needed to start breaking the bonds in the reactants.
38
What happens to the surroundings in an exothermic reaction?
They gain heat energy, increasing in temperature.
39
What happens to the surroundings in an endothermic reaction?
They lose heat energy, decreasing in temperature.
40
Why do melting and freezing not indicate a chemical reaction?
Because melting and freezing only change the physical arrangement of molecules without forming new substances; the chemical composition and molecular structures remain unchanged.
41
What does an increased temperature on a thermometer indicate?
That the surroundings are gaining thermal energy, likely from an exothermic reaction.
42
What is an example of a real-world use of exothermic reactions?
Hand warmers, self-heating cans, combustion in car engines.
43
What is an example of a real-world use of endothermic reactions?
Cold packs for sports injuries, photosynthesis in plants.
44
How do we know energy is conserved in chemical reactions?
The total energy before and after a reaction remains the same, it only changes form.
45
How many elements are there in the Periodic Table?
118
46
What is the formula of Ammonium?
NH₄⁺
47
What is the formula of Hydroxide?
OH⁻
48
What is the formula for Nitrate?
NO₃⁻
49
What is the formula for Sulfate?
SO₄²⁻
50
What is the formula for Carbonate?
CO₃²⁻
51
What is the formula for Hydrogen Carbonate?
HCO₃⁻
52
What is the formula for Phosphate?
PO₄³⁻
53
What is the Law of Conservation of Mass in chemical equations?
The same number of atoms of each element must be present on both sides of a chemical equation.
54
Which nonmetals must be written as diatomic molecules?
H₂, N₂, O₂, F₂, Cl₂, Br₂, and I₂
55
What is the general strategy for balancing chemical equations?
Work across the equation from left to right, checking one element after another. Change coefficients (multipliers) in front of formulas one by one. Balance elements that appear on their own last in the process.
56
How should you handle groups of atoms that don't change in a reaction?
Count the whole group as one entity rather than counting individual atoms (e.g., nitrate group NO₃⁻)
57
What are state symbols and why are they used?
State symbols show the physical state of each substance in a reaction: (s)=solid, (l)=liquid, (g)=gas, (aq)=aqueous solution
58
How do you balance: Al + CuO → Al₂O₃ + Cu?
2Al (s) + 3CuO (s) → Al₂O₃ (s) + 3Cu (s)
59
How do you balance: MgO + HNO₃ → Mg(NO₃)₂ + H₂O?
MgO (s) + 2HNO₃ (aq) → Mg(NO₃)₂ (aq) + H₂O (l)
60
What state are most metal compounds usually in?
Solid (s), although there are exceptions
61
What state are most ionic compounds usually in?
Solid (s)
62
What state are non-metal compounds usually in?
Could be solid (s), liquid (l), or gas (g), depending on the chemical structure
63
What is considered a precipitate and what state symbol would it have?
A solid formed in a solution; state symbol (s)
64
How do you write a balanced ionic equation?
- Balance the equation
- Identify ionic substances and write ions separately
- Remove spectator ions on both sides
- Rewrite ionic equations
65
What is a half equation?
A half equation represents what happens to one of the reactants in a chemical reaction
66
True or False: Half equations have the same coefficients as the overall equation.
False, they do not have to be the same but they do need to be balanced in atoms and charges in its own equation
67
What are chemical amounts measured in?
Moles, mol (SI unit of amount of substance)
68
What is one mole?
- Avogadro's Number/ Constant (when using mol⁻¹)
- 6.02214076× 10²³ elementary entities
OR
- 6.02 x 10²³ mol⁻¹
69
What is the mass of 1 mole of substance known as?
Molar Mass
70
What is the molar mass the same as in an element?
Same as relative atomic mass written in grams
71
How do you find the mass of one atom or molecule?
Molar Mass / Avogadro's Constant
72
What is the formula to convert between moles, mass and molar mass?
Mass
/
Molar Mass x Moles
73
What does the Law of Conservation of Mass state?
The Law of Conservation of Mass states that no matter is lost or gained during a chemical reaction.
74
Why must chemical equations be balanced?
Because mass is always conserved, and the total mass of reactants must equal the total mass of products.
75
How does the sum of relative atomic/molecular masses compare between reactants and products?
The sum of relative atomic/molecular masses of reactants equals the sum of relative atomic/molecular masses of products, accounting for stoichiometry.
76
Do changes of state affect conservation of mass?
No, changes of state do not affect the conservation of mass, but can appear to do so if gaseous products escape.
77
What happens to the total mass when a reaction occurs in a closed system?
The total mass remains constant if the reaction flask is closed and no substance can enter or leave.
78
What is a precipitation reaction?
A reaction in which two solutions react to form an insoluble solid called a precipitate.
79
Give an example of a precipitation reaction that demonstrates conservation of mass.
The reaction between calcium chloride and sodium sulfate producing calcium sulfate precipitate: CaCl2 (aq) + Na2SO4 (aq) ⟶ CaSO4 (s) + 2NaCl (aq)
80
Why might some chemical reactions appear to involve a change in mass?
Due to the presence of a gaseous reactant or product that enters or leaves the system.
81
What happens to the mass in an open system when a gaseous product is produced?
The total mass of the reaction flask will decrease as the gaseous product escapes the system.
82
Give an example of a reaction where mass appears to decrease.
The reaction between hydrochloric acid and calcium carbonate: 2HCl (aq) + CaCO3 (s) ⟶ CaCl2 (aq) + H2O (l) + CO2 (g)
83
What happens during thermal decomposition of metal carbonates regarding mass?
Carbon dioxide gas escapes, leaving only the metal oxide as solid product, creating an apparent decrease in mass.
84
When might the mass of a reaction container increase?
When one of the reactants is a gas from the air and all products are solids or liquids.
85
Give an example of a reaction where mass appears to increase.
The reaction of magnesium with oxygen: 2Mg (s) + O2 (g) → 2MgO (s)
86
What happens to the mass when iron wool rusts?
The mass increases as iron(III) oxide has a larger mass than iron: 4Fe (s) + 3O2 (g) → 2Fe2O3 (s)
87
Explain the balanced equation: CaCl2 (aq) + Na2SO4 (aq) ⟶ CaSO4 (s) + 2NaCl (aq)
Calcium chloride solution reacts with sodium sulfate solution to form solid calcium sulfate precipitate and sodium chloride solution, demonstrating conservation of mass.
88
What type of system is needed to directly observe conservation of mass?
A closed system where no substances can enter or leave.
89
Why does the rusting of iron demonstrate an increase in mass?
Because iron combines with oxygen from the air to form iron(III) oxide, which has greater mass than the original iron.
90
What is stoichiometry?
The study of the quantitative relationships between reactants and products in a chemical reaction
91
What are coefficients in a chemical equation?
Numbers placed in front of reactants and products to balance the equation
92
How do you convert mass to moles?
Divide the given mass by the molar mass of the substance
93
What is a limiting reactant?
The reactant that is completely consumed in a chemical reaction and determines the amount of product formed
94
What is an excess reactant?
The reactant that remains after the limiting reactant is completely used up
95
What are the steps to determine the limiting reactant?
1. Convert masses of reactants to moles
2. Write the balanced chemical equation
3. Determine the molar ratios
4. Compare moles of reactants based on the balanced equation
96
How do you balance an equation with uneven mole calculations?
Multiply all numbers by a common factor to get whole number coefficients
97
What does the proportionality of product mean?
The amount of product formed is directly proportional to the amount of limiting reactant
98
When does a chemical reaction stop?
When the limiting reactant is completely consumed
99
What is a molar ratio?
The relative number of moles of reactants and products in a balanced chemical equation
100
How does the limiting reactant affect product formation?
It determines the maximum amount of product that can be formed in a reaction
101
What is molar mass?
The mass of one mole of a substance
102
Why is it important to convert to moles in stoichiometric calculations?
To allow for accurate comparison of reactant quantities using their molar relationships
103
What does oxidation and reduction involve?
Addition and removal of oxygen or electrons
104
What is OILRIG?
Oxidation
Is
Loss
Reduction
Is
Gain
105
What is a redox reaction?
Reaction in which oxidation and reduction are both taking place at the same time
106
What happens when acids are added to water?
Form positively charged hydrogen ions (H⁺) making solution acidic
107
What happens when alkalis are added to water?
Form negatively charged hydroxide ions (OH⁻) making the solution an alkali
108
What is the pH scale?
Numerical scale which is used to show how acidic or alkaline a solution is
109
What are the results of the pH scale?
Lower the pH, the more acidic
Higher the pH, the more alkaline
pH of 7 is neutral
110
How can pH be measured?
Using an indicator or a digital pH meter
111
What is a digital pH meter?
Contain a special electrode with a thin glass membrane that allows hydrogen ions to pass through; the ions alter the voltage detected by the electrode
112
What is an indicator?
Substance that changes colour depending on the pH of solution which it is added
113
What are bases characterized by?
pH values above 7
114
What are alkalis?
Soluble metal hydroxides that dissolve in water
115
Give examples of alkalis
NaOH and Ca(OH)₂
116
What happens in a neutralisation reaction?
Acid and base react to produce salt and water
117
What is the general equation for neutralisation?
acid + base ⟶ salt + water
118
What is the ionic equation for neutralisation?
H⁺ + OH⁻ ⟶ H₂O
119
What determines the identity of the salt in a neutralisation reaction?
The acid used and the positive ions in the base
120
What salt do different acids produce?
Hydrochloric acid produces chlorides
121
What happens when acids react with metal carbonates?
Produces metal salt
122
What is a key characteristic of acid-metal carbonate reactions?
Effervescence (bubbling) due to carbon dioxide gas
123
What is the general equation for acid-metal carbonate reactions?
acid + metal carbonate ⟶ salt + water + carbon dioxide
124
Which metals react with dilute acids?
Metals above hydrogen in the reactivity series
125
How do the reactions of metals with acids vary?
More reactive metals have more vigorous reactions
126
What is the general equation for acid-metal reactions?
metal + acid ⟶ salt + hydrogen
127
How are salts named?
Two parts - first from the metal/metal compound
128
What does the first part of a salt's name come from?
The metal
129
What does the second part of a salt's name come from?
The acid used in the reaction
130
Why are some acid-metal reactions not considered neutralisation?
No water is formed in the reaction
131
Give an example of predicting reaction products
Magnesium carbonate + nitric acid → magnesium nitrate + carbon dioxide + water
132
What makes metals like potassium and sodium dangerous when reacting with acids?
They react explosively
133
What ion is present in chloride salts?
Cl⁻ ion
134
Example of salt formation: Sodium hydroxide and hydrochloric acid
Produces sodium chloride
135
Example of salt formation: Zinc oxide and sulfuric acid
Produces zinc sulfate
136
What are the products when copper oxide reacts with sulfuric acid?
Copper sulfate and water
137
What are the products when sodium reacts with hydrochloric acid?
Sodium chloride and hydrogen
138
What determines whether an acid is strong or weak?
The number of ions produced when dissolved in water
139
What is ionisation or dissociation?
The process of an acid breaking down into ions when added to water
140
Give an example of a strong acid dissociation equation
HCl ⟶ H⁺ + Cl⁻
141
Give an example of a weak acid dissociation equation
CH₃CH₂COOH ⇌ H⁺ + CH₃CH₂COO⁻
142
What characterizes strong acids?
Complete dissociation in water with high H⁺ ion concentration
143
What characterizes weak acids?
Partial ionisation in water with pH values between 4-6
144
What does the ⇌ symbol indicate in acid dissociation?
The process is reversible
145
Where does the equilibrium lie in weak acids?
Towards the left (more intact acid molecules)
146
What is the difference between strong and concentrated acids?
Strong refers to dissociation ability
147
How is concentration defined?
Number of acid particles in a certain volume
148
Can a solution be both concentrated and weak?
Yes
149
Can a solution be both dilute and strong?
Yes
150
What determines the pH of an acid?
The concentration of H+ ions
151
How do strong acids differ from weak acids in water?
Strong acids completely dissociate
152
Give examples of strong acids
HCl and H₂SO₄
153
Give examples of weak acids
Ethanoic acid (CH₃COOH) and hydrofluoric acid (HF)
154
What happens to weak acids in water?
An equilibrium is established between molecules and ions
155
What is the significance of the equilibrium lying to the left in weak acids?
Low ion concentration and higher pH
156
Can a dilute strong acid have a lower pH than a concentrated weak acid?
Yes
157
What determines the number of H+ ions in solution?
The type of acid (strong or weak) and its concentration
158
What is pH?
A measure of the concentration of H+ ions in solution
159
What characterizes a concentrated acid or base solution?
Contains a high number of acid or base molecules per dm3 of solution
160
What defines a dilute acid or base solution?
Has much fewer acid or base molecules per dm3 of solution
161
How is the pH scale logarithmic?
Each change of 1 on the scale represents a change in concentration by a factor of 10
162
How do H+ ion concentrations change between pH levels?
An acid with pH 3 has ten times the concentration of H+ ions compared to an acid with pH 4; an acid with pH 2 has 100 times the concentration of an acid with pH 4
163
What determines the pH of an acid?
The capacity of the acid to dissociate and put H+ ions into solution
164
What happens to pH when a base is added to an acid?
The pH increases rapidly due to a decrease in hydrogen ion concentration
165
What happens to pH when an acid is added to a base?
The pH decreases rapidly due to an increase in hydrogen ion concentration
166
What is electrolysis?
Where an electric current is passed through a molten ionic compound and the compound breaks down
167
True or False: Electrolysis does not occur with solutions
False, process occurs for aqueous solutions of ionic compounds
168
What are liquids and solutions that can conduct electricity known as?
Electrolytes
169
What compounds cannot conduct electricity?
- Covalent Compounds
- Cannot undergo electrolysis
170
What is an electrode?
A rod of metal or graphite through which an electric current flows into or out of an electrolyte
171
What is an electrolyte?
Ionic compound in molten or dissolved solution that conducts electricit
172
What is an anode?
Positive electrode of electrolysis cell
173
What is a cathode?
Negative electrode of electrolysis cell
174
What is an anion?
Negatively charged ions attracted to anode
175
What is an cation?
Positively charged ions attracted to cathode
176
Why can't ionic compounds conduct electricity?
Have no free ions that can move and carry charge
177
What is an electrolytic cell?
Name given to set-up used in electrolysis
178
Where do electrons move during electrolysis?
Power supply to cathode
179
What does an aqueous solution always contain?
Ions from dissolved ionic compound and hydrogen and hydroxide ions (produced by water in solution)
180
What occurs at the anode during electrolysis of an aqueous solution?
- Negatively charged OH⁻ and non-metal ions are attracted to anode
- If there are halide ions present, halide ion is discharged, loses electrons and form halogen
- If no halide ions are present, OH⁻ is discharged at anode, loses electrons and forms oxygen.
- In both cases, other ion remains in solution
181
What occurs at the cathode during electrolysis of an aqueous solution?
- Positively charged H⁺ and metal ions are attracted to cathode
- If metal is above hydrogen in reactivity series, hydrogen is produced causing effervescence at cathode
- If metal is below hydrogen in reactivity series, ion of that metal is discharged and accumulates at cathode
- In both cases, other ion remains in solution
182
What are inert electrodes?
- Don't take part in process
- Made from unreactive metals
- Provide surface for reactions to happen on
183
What are non-inert electrodes?
Electrodes are used which will take part in electrolysis reaction for electroplating and purifying copper
