Changes and structure Flashcards
(34 cards)
What are the two key things needed for a reaction to be successful?
Activation energy and/or correct collision geometry
How can temperature be linked with the kinetic energy of a reaction?
Temperature can be regarded as a measure of the kinetic energy of all the particles present in the reaction.
It only requires a small rise in temperature can double the rate of reaction
What is the ratio between rate of reaction and concentration?
When concentration is doubled so too is rate of reaction
What do catalysts do?
Lower the activation energy of a reaction
How do you calculate average rate of reaction?
Time interval (t2-t1)
What is the difference between homogenius and hetrogenius catalysts?
Homogenius catalysts are in the same physical state as the reactants while hetrogenius catalysts are in a different state
Enthalpy change?
Products - reactants (- = exothermic, + = endothermic)
What is the activation complex?
An unstable arrangement of atoms formed at the maximum of the potential barrier during a reaction
What is the ionisation energy?
Energy required to remove one mole of electrons from one mole of atoms in the gaseous state
Why does the first ionisation energy increase across a period?
Because as the atoms decrease in size across a the table the outermost electrons are nearer the protons/nucleus and so are more strongly attracted.
Why does the first ionisation energy decrease down a group?
Because as the atoms increase in size going down a group the outermost electrons are further away from the protons/nucleus and so they are less strongly held.
What is the electronegativity of an atom?
A measure of its pulling power/attraction for the shared electrons in a covalent bond. Elements in top right have strongest attraction while bottom left has weakest.
How does polarity occur within compounds?
If difference is > or = 0.4 then polarity occurs (the greater the electronegativity difference, the greater the ionic character).
How are ionic bonds held together?
Ions in a lattice are held together by the strong electrostatic forces of attraction between the positive and negative ions.
What are London dispersion forces?
Weakest form of intermolecular bond. Occur because the movement of electrons in the atoms and molecules causes a temporary dipole charge in one particle. this in turn causes an induced dipole in a nearby particle. The very small positive and negative charges produced then attract each other, so this is an electrostatic force of attraction.
The larger the molecule (or atom) the stronger the LDF are and the more energy needed to break them.
Yes.
Another calculate for rate of reaction
1 1
Rate = —– time = ——–
t rate
What is hardening?
Breaking double bonds in unsaturated fats with hydrogen (in presence of nickel catalyst).
What is covalent radii?
Half the distance between the nuclei of atoms joined by a covalent bond.
What is ionic radii?
Half the distance between the inter-nuclear distance of what are effectively ions. (effectively radius of atom).
What is Markownikoff’s rule?
In adding a compound, in the form H-X, to an unsymmetrical alkane, the hydrogen will always go to the carbon atom with the most number of hydrogen atoms.
What is the trend in atomic radius across a period and why?
Decreases as the charge of the nucleus increases while the number of filled electron shells remain the same. Therefore the outer electrons are more strongly attracted to the nucleus.
What is the trend in atomic radius down a group and why?
Increases as, despite an increase in nuclear charge, the further down you go the more filled electron shells. These shells shield the force of attraction between the nucleus and the outer electrons allowing them to be further away.
Trends of electronegativity in the periodic table?
Down a group = decreases
Across a period = increases
This occurs due to the same factors which affect atomic radius.
