Types of Chemical Reactions

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Questions and Answers

What is the primary product of a synthesis reaction?

Heat and light

A new substance formed (correct)

Two or more products

Water and salt

Which of the following represents a decomposition reaction?

C H 4(g) + 2O2(g) → C O2(g) + 2H 2 O (l)

AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)

AB → A + B (correct)

HCl(aq) + NaOH(s) → NaCl(aq) + H 2 O(l)

What is produced in a complete combustion reaction of methane?

Carbon monoxide and hydrogen

Only carbon dioxide

Carbon dioxide and water (correct)

Carbon and water

In a precipitation reaction, what happens when two soluble ionic compounds are mixed?

They can form an insoluble precipitate. Signup and view all the answers

What is the purpose of the salt bridge in a galvanic cell?

To maintain solution neutrality and complete the circuit. Signup and view all the answers

Which of the following correctly describes the net ionic equation presented?

It only shows the ions that participate in the formation of the product. Signup and view all the answers

Which of the following reactions identifies acid-carbonate reactions?

Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g) Signup and view all the answers

What do metal-water reactions typically produce?

Metal hydroxide and hydrogen gas Signup and view all the answers

What happens at the anode of a galvanic cell?

Oxidation occurs producing free electrons. Signup and view all the answers

How can a reaction be represented as a complete ionic equation?

By showing all ions present during the reaction. Signup and view all the answers

In a metal displacement reaction, what determines which metal will displace another?

The metal activity series Signup and view all the answers

In the context of redox reactions, which statement is accurate about half equations?

They illustrate the transfer of electrons for either oxidation or reduction. Signup and view all the answers

What is the outcome of an acid-metal reaction?

A metal salt and hydrogen gas are formed. Signup and view all the answers

What governs the filling order of atomic orbitals?

The Aufbau principle Signup and view all the answers

Which principle explains that two identical fermions cannot occupy the same quantum state?

The Pauli exclusion principle Signup and view all the answers

What is the significance of the exceptions to the Aufbau principle in the d block?

They occur because of Coulombic repulsion and energy distinctions. Signup and view all the answers

What determines the variable valency of an atom?

The maximum number of direct bonds formable. Signup and view all the answers

What happens to electrons when they receive energy?

They can become excited and move to higher energy levels. Signup and view all the answers

Which group of elements consists of f orbitals?

Lanthanides and actinides Signup and view all the answers

What is the relationship between elements in the same group of the periodic table?

They have the same number of valence electrons. Signup and view all the answers

What occurs during the de-excitation of an electron?

Energy is released in the form of light. Signup and view all the answers

What does a higher value of reduction potential indicate?

Stronger tendency to form the non-ionic form Signup and view all the answers

Which component is reduced in a galvanic cell?

The oxidizing agent Signup and view all the answers

What is the effect of increasing temperature on the rate of reaction according to collision theory?

Increases the kinetic energy of particles Signup and view all the answers

In a galvanic cell notation, what does the left side represent?

Oxidation half-cell Signup and view all the answers

How is the voltage of a galvanic cell calculated?

E total = E reduction + E oxidation Signup and view all the answers

Which of the following factors does NOT affect the rate of reaction?

Time of day Signup and view all the answers

What happens to the anode in a typical galvanic cell reaction involving zinc and copper?

It loses electrons and becomes smaller Signup and view all the answers

What is the role of a catalyst in a chemical reaction?

It speeds up the rate of reaction without being used up Signup and view all the answers

What role do catalysts play in chemical reactions?

They provide an alternative pathway with lower activation energy. Signup and view all the answers

Which of the following statements about exothermic reactions is true?

Energy released in making bonds is greater than energy needed to break bonds. Signup and view all the answers

How is the change in enthalpy (ΔH) calculated?

ΔH = H products − H reactants Signup and view all the answers

Which substance is an example of a biological catalyst?

Chlorophyll Signup and view all the answers

What does specific heat capacity measure?

The amount of heat needed to raise 1g of a substance by 1°C Signup and view all the answers

What is true about endothermic reactions?

They absorb heat and cannot be self-sustaining. Signup and view all the answers

Which of the following calculations uses the correct formula for heat of combustion?

Energy released = n × ΔH c Signup and view all the answers

Which of the following is true about heterogeneous catalysts?

They differ in phase from the reactants. Signup and view all the answers

Study Notes

Types of Reactions

Synthesis: Two or more substances combine to form a new substance. Example: A + B → AB
Decomposition: Substance breaks down into two or more substances due to heat, light or electricity. Example: AB → A + B
Acid-base (Neutralisation): Acid reacts with a base to form salt and water. Example: HCl(aq) + NaOH(s) → NaCl(aq) + H2O(l)
Combustion Reactions: Substances burn in oxygen.
- Complete Combustion: Forms carbon dioxide and water. Example: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)
- Incomplete Combustion: Forms carbon or carbon monoxide. Examples: CH4(g) + O2(g) → C(s) + 2H2O(l) and CH4(g) + 2/3O2(g) → CO(g) + 2H2O(l)
Precipitation Reactions (Double Displacement): Two soluble ionic compounds react to form an insoluble precipitate (ppt) or mix completely. Example: AB + CD → AD + CB
- Precipitation Example: AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)
Acid-carbonate reactions: Acid reacts with carbonate to form water, salt, and carbon dioxide. Example: Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
Metal - Oxygen Reactions: Metal burns in oxygen to form a metal oxide. Example: 2Mg(s) + O2(g) → 2MgO(s)
Metal - Water Reactions: Metal reacts with water to form a metal hydroxide and hydrogen gas. Example: 2Na(s) + 2H2O(l) → 2NaOH(s) + H2(g)
Acid-metal Reactions: Acid reacts with metal to form a metal salt and hydrogen gas. Example: Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
Metal Displacement Reactions: More reactive metal displaces a less reactive metal in a compound. Example: A + BC → AC + B
- Displacement Example: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
- Metal reactivity determined by the metal activity series or reduction potentials table. Lower ionisation energy, larger atomic radius, and lower electronegativities indicate higher reactivity.

Atomic Structure

Principal Energy Levels (1, 2, 3…): Groupings of sublevels (s, p, d, f) with similar energy.
Sublevels (s, p, d, f): Groupings of individual orbital lobes.
Aufbau Principle: Electrons fill lowest available energy levels first before occupying higher levels.
Exceptions to Aufbau Principle: Occur in the d block due to reduced energy difference between s and d levels, causing Coulombic repulsion. Examples: Cu, Ag, Cr.
Heisenberg Uncertainty Principle: The position and momentum of a particle (like an electron) cannot be measured accurately at the same time.
Pauli Exclusion Principle & Hund's Rule: Each orbital within an energy level is filled first by electrons with spin +1/2 and then completed with electrons of -1/2 spin (identical fermions cannot occupy the same quantum state within the same system). Example: Oxygen
Valence Electrons: Electrons in the outermost shell of an atom.
Valency: Maximum number of direct bonds that an element can form. Variable valency can occur when an atom loses or gains more electrons than its valence shell.
Orbital Notation: Determined by filling orbitals based on the number of electrons or using spdf blocks on the periodic table.
- Helium and groups 1 and 2: s orbitals from energy levels 1-7
- Transition metals: d orbitals from energy levels 3-6
- Groups 13-18 (excluding Helium): p orbitals from energy levels 2-7
- Lanthanides and Actinides: f orbitals from energy levels 4-5

Atomic Emission Spectra and Flame Tests

Excitation: Electrons gain energy, move to a higher energy level.
De-excitation: Excited electrons return to their ground state, releasing energy as different wavelengths of light.

Redox Reactions

Half-Equations: Show electron transfer.
Neutral Species Equations: Show compounds involved.
Complete Ionic Equation: Shows all ions in the reaction mixture.
Net Ionic Equation: Shows only the ions undergoing the reaction, excluding spectator ions.
Deriving Equations:
1. Balanced Formula (Neutral Species) Equation: 2KI(aq) + Pb(NO2)3(aq) → PbI2(s) + 2KNO3(aq)
2. Total Ionic Equation (Complete Ionic): 2K+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) → PbI2(s) + 2K+(aq) + 2NO3-(aq)
3. Net Ionic Equation: Pb2+(aq) + 2I-(aq) → PbI2(s)

Galvanic Cells and Standard Electrode Potentials

Galvanic Cells: Generate electricity via redox reactions.
- Anode: Oxidation occurs, producing free electrons in the more reactive metal.
- Cathode: Electrons flow to the cathode, resulting in reduction.
- Salt Bridge: Completes the circuit, conserving solution neutrality.
  - Anions flow toward the anode to balance positive ions.
  - Cations flow toward the cathode to balance negative charges.
Standard Hydrogen Half-Cell: Platinum metal in a 1 mol/L H+ solution with hydrogen gas bubbled over at 100 kPa.
Standard Electrode Potentials: Higher values indicate a stronger tendency to form the non-ionic form; lower values suggest a tendency to form ions.
Voltage of a Galvanic Cell under Standard Conditions: Etotal = E°reduction + E°oxidation
- Galvanic cells are spontaneous when cell voltage is positive.
- Oxidizing agents are reduced, and vice versa.
Galvanic Cell Notation: X(s) | X+(aq) || Y+(aq) | Y(s) with the anode/oxidation on the left.
Galvanic Cell Example:
- Copper gains electrons at the cathode.
- Zinc loses electrons at the anode.
- Notation for Zn(s) | Zn2+(aq)(1M) || Cu2+(aq)(1M) | Cu(s)

Rates of Reactions

Collision Theory: Reactions occur due to collisions between reactant particles.
- Requires:
  - Collisions between particles
  - Sufficient energy to break bonds and reach activation energy
  - Correct orientation to break bonds and form products
Activation Energy: Minimum energy required for a collision to lead to reaction.
Measuring Reaction Rates: Use time or loss of mass.
Factors Influencing Reaction Rates:
- Surface Area: Higher surface area leads to more collisions.
- Temperature: Higher temperature increases kinetic energy, increasing collision probability.
- Concentration: Higher concentration means more particles, increasing collision probability.
- Pressure (Gases): Higher pressure brings particles closer, increasing collision probability.
- Presence of a Catalyst: Catalysts speed up reactions, but are not consumed. They provide an alternative pathway with lower activation energy.
- Examples:
  - Iron (Fe) in ammonia production: N2(g) + 3H2(g) → 2NH3(g) ΔH = -92 kJ/mol
  - Platinum (Pt) in carbon monoxide to carbon dioxide: CO(g) + 1/2 O2(g) → CO2(g)
  - Potassium permanganate (KMnO4) in hydrogen peroxide decomposition: 2H2O2(aq) → 2H2O(l) + O2(g)
  - Chlorophyll in leaves for photosynthesis
- Heterogeneous Catalysts: Different phase from reactants (e.g. gas - liquid)
- Homogeneous Catalysts: Same phase as reactants (e.g. liquid - liquid)
- Homogeneous Reactions: Occur in a single phase (e.g. liquid - liquid)

Drivers of Reactions

Chemical Potential Energy: All substances hold chemical potential energy.
Bond Breaking: Requires energy.
Bond Making: Releases energy.
Exothermic Reactions: Release heat into the surroundings.
- Energy released during bond making is greater than the energy needed to break bonds.
Endothermic Reactions: Absorb heat from the surroundings.
- Energy required to break bonds is greater than the energy released during bond making.
Enthalpy: Total heat content of a system, measured in joules (J).
Change in Enthalpy (ΔH): ΔH = Hproducts - Hreactants where H is heat content.
Heat of Combustion (ΔHc): Energy released when 1 mol of a substance combusts completely at SLC.
- Energy released for n moles of fuel burning: Energy released = n x ΔHc (when ΔHc is known)
Determining Heat of Combustion Experimentally: q = mcΔT where q is energy, c is specific heat capacity (often 4.18 for water), and ΔT is temperature change.
Specific Heat Capacity: Amount of energy to raise the temperature of 1g of a substance by 1K. Water has a high specific heat capacity (4.18), requiring lots of energy for temperature increases.

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Description

This quiz covers the various types of chemical reactions including synthesis, decomposition, acid-base, combustion, and precipitation reactions. Understand the examples and characteristics of each reaction type to enhance your chemistry knowledge. Test your comprehension with this engaging quiz!