Chemistry 9 Flashcards
Rate and extent of chemical reactions
How do you find the mean rate of reaction?
quantity of reactant used / time taken
or
quantity of product formed / time taken
What is the quantity of reactant/product formed measured in?
Mass: grams
Volume: cm³
moles
What are the units for the rate of reaction?
g/s
or
cm³/s
mol/s
What can affect the rate of chemical reactions?
The concentrations of reactants in the solution The pressure of reacting gases The surface area of solid reactants The temperature The presence of catalysts
What would happen if the concentration of a reacting solution or the pressure of a reacting gas is increased?
The reactant particles become more crowded
The frequency of collisions between reactant particles increases
The rate of reaction increases
What is a reactant?
Substances that are present at the start of a chemical reaction.
What is a catalyst?
A catalyst is a substance that can increase the rate of reaction. Catalysts are not used up during the reaction. They do not alter the products of the reaction. Different reactions need different catalysts.
_______ act as catalysts in biological systems.
Enzymes
Changing the temperature affects…
the frequency of collisions
The energy of collisions
The rate of reaction
Changing the concentration affects…
the frequency of collisions of dissolved reactants
Changing the surface area affects…
the frequency of collisions involving a solid reactant.
A chemical reaction can only take place when…
Reactant particles collide with each other
The particles have enough energy for them to react
What is activation energy?
The minimum amount of energy that colliding particles must have for them to react.
Reactions that occur slowly have…
Reactions that happen quickly have…
a low rate of reaction, e.g. rusting.
a high rate of reaction, e.g. burning and explosions.
What would happen if we increase the temperature (in an experiment)?
The frequency of collisions increases and the collisions become more energetic which increases the rate of reaction.
What would happen if we increase the concentration of reactants in a solution, the pressure of reacting gases or the surface area of solid reactants?
The frequency of collisions increases which increases the rate of reaction.
In some chemical reactions, the products of the reaction can react to produce the original reactants. Such reactions are called reversible reactions.
1) How can we represent these ‘reversible reactions’?
2) How can we change the direction of reversible reactions? Give an example of this.
1) A + B ⇌ C + D
(reactants) (products)
2) By changing the conditions, e.g.
heat
ammonium chloride ⇌ ammonia + hydrogen chloride
cool
If a reversible reaction is __________ in one direction, it is ___________ in the opposite direction. The ____ amount of energy is transferred in each case.
exothermic, endothermic } vice versa, e.g.
endothermic hydrated copper sulphate ⇌ anhydrous copper sulphate + water
exothermic
If the concentration of a product is decreased, what will happen?
More reactants will react until equilibrium is reached again.
What is the rate of reaction?
The measure of how quickly a reactant is use up or how quickly a product is formed.
What can the gradient of a line show in terms of the rate of reaction?
The steeper the line, the greater the rate for reaction
Fast reaction - line becomes horizontal or when it finished sooner than slow reactions
The greater the frequency of successful collisions then…
the greater the rate of reaction.
What would happen if a large lump is divided or ground into a powder?
Its total volume stays the dame
The area if exposed surface increase
The surface area to volume ratio increases
How do catalysts work?
They provide a different reaction pathway for the reaction that has a lower activation energy than the uncatalysed reaction.
What apparatus would we need to investigate the effect of changing the concentration on the rate of a reaction?
Trough Dilute (hydrochloric) acid Magnesium ribbon Delivery tube Conical flask Bung Measuring cylinder Clamp
What apparatus would we need to investigate the effect of changing the temperature on the rate of a reaction?
Dilute (hydrochloric) acid Sodium thiosulfate Stop clock Thermometer Paper with cross drawn on Conical flask
You are asked to create a graph from the results of a previous rate of reaction experiment.
1) What axis would time and volume produced go on and what could they be measured in?
2) What should you do to find the gradient?
1) Time (s) - x axis
Volume produced (cm3) - y axis
2) Draw the line of best fit
For 200 million years the proportions of different gases in the atmosphere have been much the same as they are today:
4/5 (approx. 80%) nitrogen
1/5 (approx. 20%) oxygen
Small proportions of various other gases including CO2, water vapour and noble gases (group 0)
Suggest one theory about the earth’ early atmosphere. State when the oxygen and carbon dioxide levels increase or decrease.
During the first billion years, there was intense volcanic activity that released gases such as H2O (water vapour), methane, ammonia, carbon dioxide and nitrogen. No oxygen was released. CO2 levels increase as a large amount as released.
As the earth cooled down, the water vapour condensed to form oceans (condensation = gas > liquid). When the oceans formed the carbon dioxide dissolved in the water to form carbonate compounds (here the CO2 levels decreased).
Sediments were formed when carbonates were produced. The sediments formed into sedimentary rocks (e.g. limestone) through pressure.
How did oxygen increase in the early atmosphere?
The first life forms on earth appeared ver 3.5billion years ago, they could live anaerobically (without oxygen). Algae first produced oxygen 2.7billion years ago by using photosynthesis (carbon dioxide + water → glucose + oxygen). Here CO2 levels decreased whilst O2 levels increased.
Over the next billion years, plants evolved and the percentage of oxygen gradually increased to a level that enabled animals to evolve.
How did carbon dioxide decrease in the early atmosphere?
Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.
Also, the formation of sedimentary rocks and fossil fuels also caused the CO2 levels to decrease because they contain carbon.
Greenhouse gases in the atmosphere…
maintain temperatures on Earth high enough to support life.
Give some examples of greenhouse gases that are present in the atmosphere.
Carbon dioxide
Methane
Water vapour
What do water vapour, carbon dioxide and methane (greenhouse gases) do?
1) They absorb heat radiated from the Earth
2) Then they release energy in all directions which keeps the Earth warm
What is the greenhouse effect?
The retention of heat in the atmosphere caused by the build-up of greenhouse gases.
Explain the greenhouse effect.
1) Electromagnetic radiation at most wavelengths passes through the Earth’s atmosphere.
2) The Earth absorbs most of the radiation and warms up.
3) The Earth radiates energy as infrared radiation.
4) Some of the infrared radiation goes into space.
5) Some of the infrared radiation is absorbed by greenhouse gases in the atmosphere.
6) The lower atmosphere warms up.
Name two activities which increase the amount of carbon dioxide in the atmosphere.
Burning fossil fuels in vehicles and power stations releases carbon dioxide
Deforestation releases carbon dioxide and reduces the absorption of carbon dioxide through photosynthesis
Name two activities which increase the amount of methane in the atmosphere.
Farming cattle
Farming rice in paddy fields
Name four potential effects of global climate change/warming.
Glaciers and polar ice melting
Sea levels rising
Patterns of rainfall changing, producing floods or droughts
Habitats changing
Suggest two reasons why climate change leads to rising sea levels.
Water from melting glaciers and polar ice enters the oceans. As the Earth’s temperature increases, seawater warms up and expands.
Define carbon footprint.
A measure of how much carbon is used through the activities of a person, company or country.
How could someone reduce their carbon footprint?
Fit photovoltaic solar panels onto the roof of their house, which will reduce the amount of electricity they use which has been generated from fossil fuels.
Commute to work by bicycle instead of driving.
Improve their home insulation (eg loft insulation or double glazing) which will reduce the amount of gas burned in the boiler.
1) a. When a fuel is burned, what gases may be released into the atmosphere?
1) b. Which of these are atmospheric pollutants?
2) What else would be released?
1)a. Carbon dioxide
Water vapour
Carbon monoxide
Sulfur dioxide
Oxides of nitrogen
1)b. Carbon monoxide
Sulfur dioxide
Oxides of nitrogen
2) Solid particles
Unburned hydrocarbons
How is carbon monoxide produced from burning fuels?
Incomplete combustion of any fuel containing carbon atoms
How is soot/particulate carbon produced from burning fuels?
Incomplete combustion of any fuel containing carbon atoms
How is sulfur dioxide produced from burning fuels?
Combustion of a fossil fuel which contains sulfur impurities
How are nitrogen oxides/oxides of nitrogen produced from burning fuels?
Oxidation of atmospheric nitrogen inside the engine of a car, lorry, etc.
Give some info on carbon monoxide.
Toxic gas
Colourless and odourless so it is not easily detected
Give some info on sulfur dioxide and nitrogen oxides
Causes respiratory problems in humans
Causes acid rain
Give some info on particulates.
Cause global dimming
Causes heath problems for humans
Product
A substance formed in a chemical reaction.
