Chemistry revision Flashcards
(29 cards)
What does the rate of a chemical reaction measure, and what are two ways to calculate it?
It measures how quickly reactants are converted into products. You can calculate it by:
Rate = amount of reactant used ÷ time
Rate = amount of product formed ÷ time
How does increasing the temperature affect the rate of reaction on a particle level?
It gives particles more kinetic energy, so they move faster, collide more frequently, and more of those collisions have energy equal to or greater than the activation energy, increasing the reaction rate.
Why does increasing the concentration or pressure increase the rate of reaction?
It increases the number of particles in a given volume, leading to more frequent collisions and a faster reaction rate.
Explain how surface area affects the rate of reaction using a solid reactant.
A larger surface area (e.g., powdered solids) exposes more particles to the surrounding reactants, increasing the number of successful collisions per second.
What is a catalyst and how does it work?
A catalyst is a substance that speeds up a chemical reaction by providing an alternative reaction pathway with a lower activation energy. It is not used up in the reaction.
How do you find the rate of reaction from a graph?
The rate at any point is the gradient (slope) of the graph. A steeper gradient means a faster reaction. For instantaneous rate, draw a tangent at that point.
What are alkanes and what is their general formula?
Alkanes are saturated hydrocarbons (only single C–C bonds). Their general formula is CₙH₂ₙ₊₂.
What are alkenes and how do they differ from alkanes?
Alkenes are unsaturated hydrocarbons with at least one C=C double bond. Their general formula is CₙH₂ₙ.
How can you test for the presence of an alkene?
Add bromine water. It turns from orange to colourless in the presence of an alkene due to an addition reaction.
What is crude oil, and how was it formed?
Crude oil is a complex mixture of hydrocarbons formed from the remains of ancient marine organisms buried under sediment and subjected to high pressure and temperature over millions of years.
How does fractional distillation of crude oil work?
Crude oil is heated until it vaporises. Vapours enter a fractionating column. Different hydrocarbons condense at different levels based on boiling points. Shorter chains condense higher up (lower boiling points).
What are the products of complete and incomplete combustion of hydrocarbons?
Complete combustion: carbon dioxide and water.
Incomplete combustion: carbon monoxide, water, and sometimes carbon (soot).
What is cracking and why is it important?
Cracking breaks long-chain alkanes into shorter alkanes and alkenes. It provides useful fuels and alkenes for making plastics. Conditions: heat, catalyst (e.g. alumina).
What is the difference between a pure substance and a mixture in chemistry?
A pure substance contains only one type of element or compound. A mixture contains two or more substances that are not chemically bonded.
How does paper chromatography work and what can it show?
It separates components of a mixture based on solubility and attraction to the stationary phase (paper). Each substance moves a different distance. The number of spots shows how many substances are present.
What is an Rf value in chromatography, and how is it calculated?
Rf = distance moved by substance ÷ distance moved by solvent front. It’s used to identify substances by comparing with known values.
What are the standard gas tests and their results?
Hydrogen: Lit splint → squeaky pop
Oxygen: Glowing splint → relights
Carbon dioxide: Bubble through limewater → turns cloudy
Chlorine: Damp litmus paper → bleached white
What flame colours do metal ions produce?
Lithium (Li⁺): Crimson
Sodium (Na⁺): Yellow/orange
Potassium (K⁺): Lilac
Calcium (Ca²⁺): Orange-red
Copper (Cu²⁺): Green
What are the colours of precipitates formed in NaOH test for metal ions?
Cu²⁺ → Blue precipitate
Fe²⁺ → Green precipitate
Fe³⁺ → Brown precipitate
Al³⁺ → White precipitate (dissolves in excess)
Mg²⁺ and Ca²⁺ → White precipitate (do not dissolve in excess)
Describe Earth’s early atmosphere and how it changed over time.
Early atmosphere was mostly carbon dioxide, with little/no oxygen and small amounts of water vapour, ammonia, and methane. Oxygen increased due to photosynthesis. Carbon dioxide decreased by dissolving in oceans, forming carbonates, and being used in photosynthesis.
What are greenhouse gases and how do they cause global warming?
Greenhouse gases (e.g., CO₂, CH₄, H₂O vapour) trap infrared radiation from Earth’s surface, warming the planet. This is called the greenhouse effect.
What human activities increase greenhouse gas levels?
Burning fossil fuels (releases CO₂), deforestation (less CO₂ absorbed), agriculture (methane from livestock and rice fields), and landfill (methane from decay).
What are the potential consequences of climate change?
Rising sea levels, more extreme weather, habitat loss, ocean acidification, and food insecurity.
What is the difference between a finite and renewable resource?
Finite resources (e.g., fossil fuels) are non-renewable and will eventually run out. Renewable resources (e.g., solar energy, biofuels) can be replenished naturally.
