Air and water

"What are the three states of matter?"

"Solid, liquid, and gas"

"At what point does melting and freezing occur?"

"Melting point"

"At what point does boiling and condensing occur?"

"Boiling point"

"How can particles be represented in the simple particle model?"

"Small solid spheres"

"What is a chemical change?"

"A change that requires a chemical reaction; reactants turn into products with chemically different properties"

"What is a physical change?"

"A change involving energy and change of state, such as melting, boiling, freezing, or condensing"

"Why do particles have different properties from the bulk substance?"

"Because of their high surface area to volume ratio; smaller quantities can be more effective"

"What is a limitation of the particle model in representing changes of state?"

"It does not account for forces of attraction between particles or the size/space of particles"

"How does the strength of forces between particles affect melting and boiling points?"

"Stronger forces = higher melting and boiling points; weaker forces = lower points"

"What happens to energy during melting or boiling?"

"Energy is transferred TO the compound"

"What happens to energy during freezing or condensing?"

"Energy is transferred FROM the compound"

"How do you predict the state of a substance given a temperature?"

"Below melting point: solid; between melting and boiling: liquid; above boiling: gas"

"What is the evidence for the formation of Earth's early atmosphere?"

"Volcanic activity released gases like CO2, N2, CH4, NH3; water vapour condensed to form oceans"

"How did oxygen gradually accumulate in Earth's atmosphere?"

"Algae and plants produced oxygen via photosynthesis, increasing O2 over billions of years"

"Major sources of carbon monoxide and particulates?"

"Incomplete combustion"

"Major source of sulfur dioxide?"

"Combustion of sulfur impurities in fuels"

"Major sources of oxides of nitrogen?"

"Oxidation of nitrogen at high temperatures and further oxidation in the air"

"Problems caused by increased sulfur dioxide

oxides of nitrogen, and carbon monoxide?","Acid rain, global dimming, and toxicity causing breathing difficulties"

"Methods to reduce emissions of these substances?"

"Catalytic converters, low sulfur petrol, gas scrubbers"

"What is an element?"

"A substance that cannot be broken down chemically, made of one type of atom, represented by a symbol (e.g., H, K)"

"What is a compound?"

"A substance made of two or more different atoms chemically joined, with different properties (e.g., H2O)"

"What is the law of conservation of mass?"

"No atoms are lost or made in a chemical reaction; mass of products = mass of reactants"

"How do you balance a chemical equation?"

"Ensure the number of each atom is equal on both sides, considering subscripts and coefficients"

"How can oxygen be tested in the lab?"

"Insert a glowing splint into the gas; it relights in oxygen"

"How can hydrogen be tested in the lab?"

"Use a burning splint at the open end; produces a 'squeaky pop'"

"How can carbon dioxide be tested in the lab?"

"Bubble through limewater; it turns milky"

"What is oxidation?"

"Gain of oxygen"

"What is reduction?"

"Loss of oxygen"

"What is an exothermic reaction?"

"Transfers energy to surroundings; surroundings' temperature increases (e.g., combustion, neutralisation)"

"What is an endothermic reaction?"

"Takes in energy from surroundings; surroundings' temperature decreases (e.g., thermal decomposition)"

"What is activation energy?"

"Minimum energy required for a reaction to occur"

"In an energy profile

how can you identify an exothermic reaction?","Products have less energy than reactants; energy is released"

"In an energy profile

how can you identify an endothermic reaction?","Products have more energy than reactants; energy is absorbed"

"How is energy change in a reaction calculated from bond energies?"

"Energy to break bonds minus energy released in forming bonds"

"Describe how to determine if a reaction is exo- or endothermic experimentally"

"Measure temperature before and during the reaction; increase = exothermic, decrease = endothermic"

"What does a chemical cell do?"

"Produces a potential difference until reactants are used up; electrons flow from more to less reactive metal"

"What are greenhouse gases and their effect?"

"Water vapour, CO2, CH4; absorb infrared radiation, warming the atmosphere (greenhouse effect)"

"What human activities increase CO2 and CH4 levels?"

"Driving (CO2) and livestock farming (CH4)"

"Effects of increased CO2 and CH4 on climate?"

"Extinction of species, sea level rise, extreme weather, decreased crop yield, migration, increased UV exposure"

"How can the effects of greenhouse gases be mitigated?"

"Use cars less, switch to hydrogen or biofuels, consider scale, risk, and environmental impact"

"Methods to make potable water from waste or ground water?"

"Sedimentation, filtration, chlorination"

"How can seawater be made potable?"

"Filter, boil to produce vapor, condense the vapor"

"Why must water used in chemical analysis be pure?"

"Dissolved salts could react and give false results"

"How can chlorine be identified in a test?"

"Damp blue litmus paper is bleached and turns white"