Unit 1 Flashcards
Steps to Reacting Masses Calculations
Identify two chemicals and write mole statement, convert moles to GFM and use proportion to calculate answer
Reaction rates can be ______ by chemists
Controlled
Rates of reaction can be affected by changes in…
Pressure, Particle Size, Temperature, Catalysts and Concentration
If reaction rates are too low a manufacturing process will not be ______
Economically Viable
If reaction rates are too high there’s a high risk of _____
Thermal Explosion
Where’s a reactions rate the quickest and why?
At the start of the reaction and as there’s the highest concentration of reactants
Calculating Average Rate
Change in concentration or mass or volume/ Time OR 1/Time
Collision Theory
States that reactants must collide with correct geometry and posses a minimum energy (Activation Energy) before a successful reaction occurs
In a dilute solution, particles are __A__ apart, meaning ___B___ likely to collide and react
A= Further B= Less
In a concentrated solution, ___A___ particles are present in the same volume. They are __B__ likely to meet and react
A = More B = More
(Using the Collision Theory) Explain why increasing the concentration increases the rate
It increases the number of particles, meaning more successful collisions
(Using the Collision Theory) Explain why increasing the pressure of a gas increases the rate
This increases the concentration of the gas, meaning more successful collisions
(Using the Collision Theory) Explain why decreasing the particle size increases the rate
This increases the surface area of the reactant, meaning more successful collisions
Temperature
A measure of the average kinetic energy of the particles of a substance
Why does a 10 Degree rise in temperate double a reaction?
The average kinetic energy of the colliding particles increases. Meaning more particles collide with >/= Activation energy. Resulting in more successful collisions
Kinetic Energy
Movement
Catalysts
Increase the rate of a reaction by providing an alternative pathway with a lower activation energy
Temperate is a __A__ of the average __B__ of the particles of a substance
A= Measure B= Kinetic Energy
The activation energy is the __A__ energy required by __B__ before the reaction will occur
A= Minimum Energy B= Colliding Particles
What can be used to explain the effect of changing temperature on the kinetic energy of particles?
An energy distribution diagram
Potential energy diagrams show the __A__ change that occurs in a reaction and the __B__
A= Enthalpy B= Activation energy
Catalysts __A__ up a reaction by __B__ the activation energy
A= Speed B= Lowering
Activated Complex
High energy with a unstable arrangement of atoms
Where’s the activated complex located?
Top of the activation energy barrier
Two types of catalysts
Heterogeneous and Homogeneous
Heterogeneous Catalysts
Catalysts that exist in a different state to the reactants
Homogeneous Catalysts
Catalysts that exist in the same state to the reactants
Exothermic reactions have a __A__ change as the products have __B__ energy as the reactants
A= Negative Enthalpy B= Less
Endothermic reactions have a __A__ change as the products have __B__ energy as the reactants
A= Positive Enthalpy B= More
To find Enthalpy change
Energy of products - Energy of reactants
To find Activation Energy
Activation Energy - Energy of Reactants
What happens when a catalyst is added to a reaction (According to potential energy diagrams)
Enthalpy stays the same, Activation energy is lowered
Elements are arranged in order of …
Increasing atomic mass and number
Periodicity
The regular recurrence of similar properties when elements are arranged in order of increasing atomic number
Explain what happens to the pattern in atomic size going across a period
The covalent atomic radius decreases because the nuclear charge increases, attracting the outer electrons more strongly, pulling them closer without any additional shielding.
Shielding
The electrons shells between the outer shell and the nucleus “Shield” (The outer electron from the nuclear charge)
Explain the pattern in atomic size going down a group
The covalent radius increases (atoms get larger) because of the addition of extra electron shells
First ionisation energy
The energy required to remove one mole of electrons from one mole of atoms in the gaseous state
Second ionisation energy
The energy required to remove one mole of electrons from one mole of 1+ ions in the gaseous state
The ____ group has the higher 1st ionisation energy
Noble gases
The ___ group has the lowest 1st ionisation energy
Alkali Metals
As you go across each period the ionisation energy ____
Increases
Why does the 1st ionisation energy increases going across a period?
Nuclear charge increases, attracting the outer electrons more strongly, meaning more energy is needed to remove the outer electron.
As you go down a group the first ionisation energy ____
Decreases
Why does the 1st ionisation energy decreases going down a group?
The energy level is further away so the electron is attached to it more strongly, meaning less energy to remove it and the outer electrons are more shielded from the nucleus
Why does the ionisation energy increases as more electrons are removed from an element?
Because of the larger attraction of the nucleus for the remaining electrons
Electronegativity
A measure of the attraction of an atom for the electrons in a bond
Across a period the electronegativity _____
Increases
Looking down a group the electronegativity _____
Decreases
Why is there no electronegativity value for the Noble gases?
They don’t form bonds
Intramolecular Bonds
Bonds formed between atoms to get a full outer shell
Main types of intramolecular bonds
Metallic, Ionic, Covalent (Network and Discrete)
Only ____ group can’t form intramolecular bonds
The noble gases
Structure of Metallic Bonds
Giant metallic lattice of positive ions in a sea of delocalised outer electrons
Delocalised
Free to Move
Definition of Metallic Bonds
Electrostatic attraction between positive ions and delocalised outer electrons
Metallic bonds are found in ….
Liquid and Solid Metals
Strength of Metallic Bonds
Varies but mostly strong
Metallic bonds get __A__ as you go down a group because the electrons are __B__ from the nuclear charge and are __C__ strongly attracted
A= Weaker B= Further C= Less
Properties of Metallic Bonds
- Conducts electricity because delocalised electrons are free to move
- Most have high mpts and bpts due to strong metallic bonds
Structure of ionic bonds
Lattice of positive and negative ions
Definition of ionic Bonds
The electrostatic attraction between positive and negative ions
Ionic bonds are found in….
Compounds containing metal/ammonium and a non-metal
Strength of Ionic bonds
Very strong bonds leading to high mpts and bpts
Properties of ionic bonds
- Conducts when molten in ‘aq’ solution as the ions are free to move
- Soluble in water
The formula of ionic bonds
Ratio of -
1 grain of salt : 2+ and negative ions
Structure of covalent network bonds
A giant lattice of covalently bonded atoms
Diamond is a covalent network bond. Properties:
Very Hard
Graphite is also a covalent network bond. Properties:
Weak forces between the layers make it soft and flaky
Properties of covalent network bonds
- Used as abrasives as they’re very hard
- Most are non-conductors (Except graphite)
- Very high mpts and bpts
Only three elements with covalent network structures
- Boron
- Carbon(Graphite and Diamond)
- Silicon(Silicon Carbide and Silicon Dioxide)
Structure of Covalent Discrete Bonds
Discrete molecules held together by weak intermolecular forces
Most covalent substances are made up of covalent __A__ molecules. These can be compounds involving __B__
A= Discrete B= Non- Metals
Discrete
There is a definite number of atoms bonded together in a molecule
Properties of a covalent discrete bond
- Low mpt and bpt
- Non-Conductor
Ionic Character
The greater the difference int he electronegativity, the more ionic character it has
Pure covalent bond
The electronegativities of both atoms are identical and the bonding electrons are shared equally between both atoms.
Polar Covalent Bonds
When there is small difference between the electronegativites of both non-metal atoms in the covalent bond
Order of ionic character between pure covalent bonds, ionic bonds and polar covalent bonds
Pure covalent bonds, polar covalent bonds and ionic character.
The three Van Der Waals Forces
- Ldf Forces
- Permanent dipole-Permanent dipole interactions
- Hydrogen Bonding
London Dispersion forces
The result of electrostatic attraction between temporary dipoles and induced dipoles and are caused by the continual movement of electrons in atoms and molecules
How ldf arise
- The electron cloud around the molecule or atom won’t be symmetrical. Meaning a more negative charge on one side of a molecule giving it a temporary dipole
- This dipole then induces dipoles in neighbouring molecules or atoms. The small positive end attracts to the small negative end of the induced dipole
Ldf are the only bond found between __A__. Polar molecules can have __B__ intermolecular forces between them.
A= Non- Polar Molecules B= Additional
Ldf are _____ than covalent bonds
Weaker
Why is it that the larger the molecule of atom, the stronger the ldf?
The electron cloud is larger and has a higher number of temporary dipoles available to induce dipoles in neighbouring molecules or atoms
The higher the ldf, the ___ the boiling point
Higher
As you go down group 7, the molecule __A__ and the strength of the ldf __B__
A & B= Increases
Permanent dipole - permanent dipole interactions
Additional electrostatic forces of attraction between polar molecules
To find out if a molecule has permanent dipole-permanent dipole interactions
- Use electronegativities to see whether they are pure or polar covalent
- Work out the GFM
Hydrogen Bonds
Intermolecular forces which are formed between molecules in which hydrogen is bonded to a strongly electronegative atom like fluorine, oxygen or nitrogen
When hydrogen bonds are present, the substance will have a __A__ mpt and bpt than another substance of __B__ mass
A= Higher B= Similar
Hydrogen bonds are the ___ intermolecular bond
Strongest
Properties of water that are affected by hydrogen bonding
- High mpt and bpt
- Surface tension
- It’s more viscous than ethanol
- Water is miscible with methanol but immiscible with tetrachloromethane
- The density of ice is less than water at low temperatures
- Water is less volatile
Why is there high mpts and bpts in water
There’s a lot of strong hydrogen bonds between the molecules and must be broken before ice can melt and water can boil
Why has water got surface tension
Because of hydrogen bonds
Why is water more viscous than ethanol
As it has more hydrogen bonds between the molecules
Surface tension
Acts as if it’s surface is encloses in an elastic skin
Viscous
It’s molecules can’t flow over one another as easily, making it thicker
As the number of O-H groups increases, the amount of hydrogen bonds __A__ and the viscosity __B__
A & B = Increases
Miscible
Mixes
Immiscible
Doesn’t mix
Why is water more miscible with methanol than with tetrachloromethane?
It has the same type of intermolecular forces
Water is _____ with liquids with weak intermolecular forces
Immiscible
What type of liquid would be miscible with tetracholoromethane?
Another non-polar covalent molecule
Why does ice float on water?
Ice is less dense than water because in ice the water molecules form an open lattice structure held together by lots of hydrogen bonds
Why is water less volatile than ethanol?
Water forms more hydrogen bonds, meaning more energy is needed for the molecules to separate
Volatile
Evaporates less easily
What molecules or compounds dissolve best in polar solvents like water and alcohols?
- Ionic compounds
- Polar Molecules
What dissolves best in non-polar solvents?
Non-polar compounds
What needs to happen for a solute to dissolve in a solvent?
Enough energy must be releases when new bonds form between the solvent and solute to break the bonds between the solute particles
How are all acids formed
By dissolving polar covalent molecules in water
Hydrogen Chloride (HCl) dissolves to form…
Hydrochloric Acid
Hydrogen Nitrate (HNO3) dissolves to form…
Nitric Acid
Hydrogen Sulphate (H2SO4) dissolves to form…
Sulphuric Acid
Why can an ionic compound dissolve in water
The attraction between the ions and the polar bonds in water molecules release enough energy to break up the ionic lattice
Why can a polar covalent compound dissolve in water?
The attraction between the polar molecule and water molecules release enough energy to break up the covalent bonds in the molecule
Why are ionic compounds insoluble in non-polar solvents?
The non-polar molecules mean they can’t attract ions strongly to break up the ionic lattice
Why are non- polar substances insoluble in water?
There’s no strong attraction between non-polar molecules and water, so there’s not enough energy released to break the covalent bonds within it
Why are non- polar substances soluble in non-polar solvents?
When new ldf form between the two molecules, enough energy is released to break the ldf between the non-polar substances
Elements with high mpt and bpt have….
Strong metallic or covalent (Network) bonds
Elements with low mpt and bpt have…
Ldf
In general the mpt and bpt of elements __A__ across period 2 and 3 reaching a __B__ at group 4
A= Increases B= Peak
Why does the metallic bonds increases going across a period?
- The charge of the ion increases
- The number of outer electrons which become delocalised increases
What happens to the mpt and bpt in Group 4?
It has the highest mpt and bpt because lots of covalent bonds have to be broken when it melts or boils
Why is H and He in period 1 and elements in group 5 to 0 have low mpt and bpt?
- In group 0, weak ldf must be broken between the atoms
- H2, Group 5,6, and 7 elements must have broke ldf between the molecules
Explain the mpt and bpt going down group 1
It decreases because the metallic bonds get weaker
Explain the mpt and bpt as you go down group 7
The mpt and bpt increase because the molecules get larger, increasing the surface area and strength of ldf
Sublime
They change directly from a solid into a gas
Which elements are in sublime
Carbon and Arsenic
