Unit 3 - Chemistry In Society Flashcards
How can you tell if a reactant is in excess
There is too much of the chemical and some is left over after the reaction
How can you tell if a reactant is a limiting reactant
The reactant is all used up after the reaction. The chemical reaction stops
How would you calculate the number of moles present
- work out formula
- work out ration of ions
What is the molar volume
One mole of all gases, at the same temperature and pressure, have the same volume
How can volume be calculated using molar volume
V = n x MV
What is percentage yield
Measure to show how much of the limiting reactant has been turned into the desired product
What is atom economy
Percentage of reactants that get turned into useful products
What is a sign of the reaction being more effective
Higher atom economy
What remains constant at equilibrium
Concentrations of reactants and products
When is a reaction at equilibrium
When the rates of the forward and reverse reactions are equal
What are the three factors affecting equilibrium
- concentration
- temperature
- pressure
What is Le Chatlelier’s principle
If a system at equilibrium is subjected to any change, the system will adjust itself to counteract the applied change
When the concentration of a reactant increases, in what direction does the equilibrium move
Moves to the right
When the concentration of a product increases, in what direction does the equilibrium move
Moves to the left
An increase in temperature will have what effect on the position of equilibrium
Moves in direction of endothermic reaction
A decrease in temperature will have what effect on the position of equilibrium
Moves in direction of exothermic reaction
When is a reaction endothermic
Enthalpy change = positive
When is a reaction exothermic
Enthalpy change = negative
Which side does the equilibrium move to when there is an increase in pressure
Moves to the side with less moles
Which side does the equilibrium move to when there is a decrease in pressure
Moves to side with more moles
What effect does adding a catalyst have on the position of equilibrium
No effect
What type of reaction takes in energy
Endothermic
Why might endothermic reactions be expensive to run
May incur costs to supply energy to the reaction
What type of reaction releases energy
Exothermic
What type of reaction may require the removal of heat to prevent temperatures rising
Exothermic reaction
What can be used to heat reactants instead of fuels or electricity
Heat generated from an exothermic reaction
What can be used to remove heat fro a reaction vessel
Water from rivers
Why is it important to control the temperatures of reactions
To prevent explosions
What is enthalpy of combustion
Energy released when one mole of substance burns completely in oxygen
What measurements need to be taken when measuring enthalpy of combustion
- volume of water
- mass of spirit burner at start and end
- initial and final temperature of water
Why can the experiment used to find enthalpy of combustion using a spirit burner and a copper can be inaccurate
- evaporation of alcohol
- incomplete combustion
- heat lost to surroundings
What is Hess’s law
The enthalpy change for a chemical reaction is independent of the root taken
Why is Hess’s law used
To determine enthalpy changes that cannot be measured directly
What is bond enthalpy
The energy required to break one mole of a particular bond between a pair of atoms
What is oxidation
The loss of electrons
What is a reduction reaction
The gaining of electrons
What is a redox reaction
Involves both an oxidation and a reduction reaction
How can the overall redox reaction equation be found
Combining the ion electron equations for the oxidation and reduction then balancing the electrons to cancel
What is an oxidising agent
A substance which accepts electrons
What type of reaction does an oxidising agent take part in
Reduction reaction
What is a reducing agent
Substance which donates electrons
What type of reaction does a reducing agent take part in
Oxidation reaction
What are some uses of oxidising agents
- kill fungi, bacteria and inactive viruses
- breakdown of coloured compounds (used in bleach)
In the electrochemical series which elements are more likely to be reducing agents and take part in oxidation reactions
Elements higher up in the series
What are the elements lower down in the electrochemical series likely to be
Oxidising agents, taking part in reduction reactions
How would you decide if a reaction is possible
Identify oxidation and reduction reactions then if the redox formed is the same as example then the reaction is possible
What are the steps for balancing an ion electron equation
- write equation
- balance metals/non-metals
- balance oxygens by adding H2O
- balance hydrogens
- balance charges
What is a standard solution
Solution with an accurately known concentration
What is volumetric analysis
Using a standard solution in a quantitative reaction to determine the concentration of another solution
What type of experiment is used in volumetric analysis
Titration
What must be done first before accurate readings are used
Rough titration
Why is an indicator used
Used to find end point
What could be used to achieve a precise end point.
White tile
How is a standard solution made up
- calculate mass of solid
- weigh out mass into beaker
- add water
- pour into 1 litre flask
- rinse beaker and add washings to flask
- make up to mark with water
Why is chromatography used
Used to separate and analyse mixtures
In paper chromatography what is the mobile and stationary phases
Mobile - liquid solvent
Stationary - paper
In thin-layer chromatography (TLC) what is the mobile and stationary phases
Mobile - liquid solvent
Stationary - silica on glass
In gas-liquid chromatography what is the mobile and stationary phases
Mobile - gas
Stationary - liquid stuck to solid
How does polarity affect paper chromatography
The less polar the substance the further it moves up, dissolves in solvents mobile phase
If a molecule is more polar how does this affect the distance it travels
Moves less further up, dissolves in stationary phase
What is used to reveal spots in thin-layer chromatography
A locating agent or UV light
What type of chromatography produces a graph
Gas-liquid chromatography
What does a a graph produced from gas-liquid chromatography show
- number of compounds in mixture
- how much of each compound present
- retention time
What is retention time affected by
- size of molecule
- polarity of molecule
How does the size of a molecule affect retention time
Larger molecule = longer retention time
How does the polarity of a molecule affect retention time
More polar = longer retention time
What is a raw material
Initial starting materials from which a processes feedstock is derived
What is a feedstock
Reactant from which other chemicals can be extracted or synthesised
How is a feedstock derived from a raw material
By physical separation or by chemical reaction
What must raw materials and feedstocks be to maximise profits
- readily available
- from sustainable sources
- suitable cost
What other factors must be considered to maximise profits
- recycling of materials
- energy requirements minimised
- by products sold
- high yield and maximum atom economy
What environmental considerations must be made when dealing with industrial chemical processes
- minimise production of waste
- avoid use or production of toxic materials/ those that won’t degrade in environment
