Science Chap. 2 Reaction Types (2025)

What are the two types of reactions based on energy changes?

Endothermic and Exothermic reactions.

What is an endothermic reaction?

A reaction that requires energy input to proceed, such as chemical cold packs containing ammonium nitrate and water.

What is an exothermic reaction?

A reaction that releases energy as heat or light, such as combustion reactions.

Provide an example of a combustion reaction.

Methane + oxygen → carbon dioxide + water vapour.

What is complete combustion?

A reaction that occurs when there is sufficient oxygen, producing carbon dioxide and water vapour.

What is incomplete combustion?

A reaction that occurs when oxygen is restricted, producing carbon monoxide or carbon (soot).

What is the difference between complete and incomplete combustion?

Complete combustion is cleaner and produces more energy, while incomplete combustion is dirty and produces pollutants.

What are hydrocarbons?

Highly combustible fuels that can react with oxygen to release energy, such as methane, ethane, and octane.

What greenhouse gas is released when burning fossil fuels?

Carbon dioxide.

What are the products of aerobic respiration?

Carbon dioxide and water vapour.

What is corrosion?

The process where most metals react with water, air, or chemicals to form other compounds.

What does iron corrode into when exposed to oxygen and water?

Rust, or hydrated iron(III) oxide.

What is the reaction for the corrosion of copper?

Copper + water + carbon dioxide + oxygen → copper(II) hydroxide + copper(II) carbonate.

What happens to silver when it reacts with hydrogen sulfide?

It tarnishes, forming silver sulfide and hydrogen gas.

How do sodium and potassium react with water?

They corrode rapidly, often with explosive reactions, producing sodium hydroxide or potassium hydroxide and hydrogen gas.

What protective layer does aluminium form when exposed to air?

A protective aluminium oxide layer.

What is anodising?

A process that thickens the aluminium oxide layer for additional protection.

What is the general formula for writing a balanced chemical equation?

Replace names with chemical symbols/formulas and ensure equal atoms of each element on both sides.

Provide the balanced equation for the reaction of copper with sulfur dioxide.

Cu + SO₂ → Cu₂S + O₂.

What do acids produce when they corrode metals?

A salt and hydrogen gas.

What is the general equation for the reaction of an acid with a metal?

acid + metal → salt + hydrogen gas.

Provide an example of an acid reacting with a metal, including the chemical equation.

Hydrochloric acid + magnesium → magnesium chloride + hydrogen gas: 2HCl + Mg → MgCl₂ + H₂.

What is the general equation for neutralisation reactions between acids and bases?

acid + base → salt + water.

Give an example of a neutralisation reaction, including the chemical equation.

Nitric acid + potassium oxide → potassium nitrate + water: 2HNO₃ + K₂O → 2KNO₃ + H₂O.

What happens when acids react with carbonates?

They form a salt, water, and carbon dioxide.

What is the general equation for the reaction of an acid with a carbonate?

acid + carbonate → salt + water + carbon dioxide.

Provide an example of an acid reacting with a carbonate, including the chemical equation.

Hydrochloric acid + calcium carbonate → calcium chloride + water + carbon dioxide: 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂.

What is the definition of a salt in chemistry?

A compound formed when a metal replaces hydrogen in an acid.

Name three examples of salts and their corresponding acids.

Potassium nitrate (KNO₃) from nitric acid (HNO₃), magnesium sulfate (MgSO₄) from sulfuric acid (H₂SO₄), calcium chloride (CaCl₂) from hydrochloric acid (HCl).

What role does hydrochloric acid play in digestion?

It activates pepsin, stops digestion of starch from saliva, and kills harmful microorganisms in food.

How is stomach acid neutralised in the digestive system?

Stomach acid (HCl) is neutralised by sodium hydrogen carbonate (NaHCO₃) from the pancreas in the duodenum.

Write the equation for the neutralisation of stomach acid by sodium hydrogen carbonate.

HCl + NaHCO₃ → NaCl + H₂O + CO₂.

What is the pH level in the mouth, stomach, and duodenum during digestion?

Mouth (pH ~7): slightly alkaline; Stomach (pH 0-3): strongly acidic; Duodenum (pH 7-8): neutralised by sodium hydrogen carbonate.

How can bee and wasp stings be treated using acid-base reactions?

Bee stings (acidic) can be neutralised by bases like bicarbonate of soda, while wasp stings (alkaline) can be neutralised by acids like vinegar.

What is the objective of the acid rain experiment using chalk?

To model the effects of acid rain on marble.

What materials are used in the acid rain experiment?

Lemon juice (citric acid), vinegar (ethanoic acid), water, and chalk (CaCO₃).

What is the expected outcome of the acid rain experiment?

Chalk dissolves in acids, producing CO₂ bubbles; chalk in water remains unchanged.

What is photosynthesis?

A series of chemical reactions in green plants that produce glucose (C₆H₁₂O₆), storing energy from sunlight.

What is the word equation for photosynthesis?

Carbon dioxide + water → glucose + oxygen (in the presence of sunlight and chlorophyll).

What is the balanced formula equation for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

Where does photosynthesis occur in plants?

In the chloroplasts of green plant cells.

What adaptations do leaves have to maximize light exposure?

Flattened leaves maximize light exposure; plants in hot environments have small or needle-shaped leaves to reduce water loss.

What adaptations do plants in hot environments have to reduce water loss?

They have small or needle-shaped leaves.

What type of leaves do rainforest plants have and why?

They have large, flat leaves to capture low light.

How do plants absorb water?

Water is absorbed by roots and transported to leaves.

What are stomata and their role in plants?

Stomata are tiny openings in leaves that allow carbon dioxide to enter and oxygen to exit.

What is the definition of respiration in biological terms?

Respiration is a process that releases energy from glucose in the presence of oxygen.

What is the word equation for respiration?

Glucose + oxygen → carbon dioxide + water + energy.

What is the balanced formula equation for respiration?

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.

Where does respiration occur in cells?

Respiration occurs in the mitochondria of cells.

What is the role of enzymes in respiration?

Enzymes control and speed up the reaction of respiration.

How does plant respiration differ from human respiration?

In plants, oxygen enters through stomata and lenticels, while in humans, glucose enters the blood and oxygen is absorbed in the lungs.

What is photosynthesis and where does it occur?

Photosynthesis occurs only in green plants, makes glucose, uses carbon dioxide, and produces oxygen in chloroplasts.

How does respiration differ from photosynthesis?

Respiration occurs in all living organisms, uses glucose, produces carbon dioxide and water, and releases energy continuously.

What are the uses of glucose produced by photosynthesis in plants?

Energy (respiration), storage (converted to starch), structure (cellulose), transport (sucrose), oils/proteins, and vitamins.

What role do plants play in carbon storage?

Plants act as carbon sinks, storing carbon from the atmosphere in the form of glucose.

What is the impact of deforestation on carbon storage?

Deforestation and burning release stored carbon back into the atmosphere, contributing to climate change.

What are lenticels and their function in plants?

Lenticels are openings in stems and roots that allow for gas exchange.

What is the effect of acid rain demonstrated in the acid rain experiment?

It shows the effects of acid rain on marble using chalk (calcium carbonate) in vinegar (acid).

What distinguishes chemical reactions from nuclear reactions?

Chemical reactions involve rearrangement of atoms without changing them, while nuclear reactions alter the nucleus and can change one element into another.

What is nuclear decay?

Nuclear decay is a type of nuclear reaction where an unstable nucleus emits radiation.

What are some applications of nuclear reactions?

Applications include nuclear power, cancer treatments, but also risks such as nuclear warfare and nuclear waste.

What happens to carbon dioxide produced during plant respiration?

It can be used in photosynthesis or exit the plant through stomata.

How is water transported in plants?

Water is absorbed by roots and moves through xylem to leaves.

What is transmutation in nuclear chemistry?

Transmutation is the process that changes an atom into a different element when the number of protons in the nucleus changes.

What historical attempt did alchemists make regarding transmutation?

Alchemists in the Middle Ages attempted to turn lead into gold through chemical reactions.

What are radioisotopes?

Radioisotopes are unstable atoms that undergo nuclear decay, emitting particles or electromagnetic waves.

What are isotopes?

Isotopes are different versions of the same element with the same number of protons but different numbers of neutrons.

List the three isotopes of carbon and their characteristics.

Carbon-12: 6 protons, 6 neutrons (stable); Carbon-13: 6 protons, 7 neutrons (stable); Carbon-14: 6 protons, 8 neutrons (radioactive).

What are the three main types of nuclear decay?

Alpha decay, Beta decay, Gamma decay.

What occurs during alpha decay?

Alpha decay ejects an alpha particle (2 protons and 2 neutrons) and occurs in heavy nuclei.

Provide an example of alpha decay.

Uranium-238 undergoes alpha decay to become Thorium-234, losing 2 protons and 2 neutrons.

What happens during beta decay?

In beta decay, a neutron converts into a proton, ejecting a beta particle (an electron) and increasing the atomic number by 1.

Provide an example of beta decay.

Carbon-14 undergoes beta decay to become Nitrogen-14, where a neutron becomes a proton.

What characterizes gamma decay?

Gamma decay involves no particles being emitted; instead, a high-energy electromagnetic wave (gamma ray) is released.

What is half-life in nuclear chemistry?

Half-life is the time it takes for half of a sample of radioactive nuclei to decay.

What is the half-life of Radon-222?

Radon-222 has a half-life of 4 days.

List some examples of half-lives of various isotopes.

Gold-200: 48 minutes; Radon-222: 4 days; Iodine-131: 8 days; Cobalt-60: 5.3 years; Americium-241: 460 years; Carbon-14: 5730 years; Plutonium-239: 24,000 years; Uranium-238: 4.5 million years.

What is carbon dating?

Carbon dating is used by archaeologists to determine the age of fossils and artifacts based on the decay of carbon-14 into nitrogen-14.

How does carbon-14 decay over time?

Living organisms absorb carbon-14, but when they die, absorption stops, and the amount of carbon-14 decreases over time.

What is nuclear radiation?

Nuclear radiation refers to particles and rays emitted by atomic nuclei, including alpha particles, beta particles, and gamma rays.

What are the properties of alpha particles?

Alpha particles are equivalent to a helium nucleus, travel at 10% of the speed of light, and have a charge of +2.

What are the properties of beta particles?

Beta particles are equivalent to electrons, travel at 90% of the speed of light, and have a charge of -1.

What are the properties of gamma rays?

Gamma rays are equivalent to high-energy X-rays, travel at the speed of light, and have no charge.

What are the biological effects of radiation?

Radiation can damage living cells, break biological molecules, and cause unwanted chemical reactions, leading to burns, radiation sickness, and cancer.

What is the significance of ionizing radiation?

Ionizing radiation, such as alpha, beta, and gamma rays, can ionize atoms by knocking electrons out, leading to cellular damage.

What are some uncertain genetic effects of radiation exposure?

Studies of Hiroshima & Nagasaki survivors showed no clear increase in mutations in their children, but men working with radioactive materials had a higher risk of having children with leukemia.