Rate of reactions UNIT 2

What factors influence rate of reactions

• Nature of the reactant

• concentration and pressure of gaseous reactants

• State of division

• Temperature

• Catalyst

Collison theory when Concentration increases

• Particles

• collisions

• orientation …therefore

• Rate of reaction

• No. of particles in the container increases per unit volume

• More collisions per unit time can occur between reactant particles

• The probability of the correct orientation and sufficient energy increases therefore more Effective collisions per unit of time

• Rate of reaction increases

Collision theory for state of division

• Contact surface

• Collisions

• Orientation…therefore

• Rate of reaction

• Exposed contact surface increases

• more collisions occur between the reactant particles per unit time

• Probability of correct orientation and sufficient kinetic energy increases per unit time

• Rate of reaction increases

Collison theory for Temperature

• Ave. Ek

• Collisions

• Ea

• Effective collisions

• Rate of reaction

• Ave. Ek of particles will be higher so particles will move faster

• No. of collisions between particles will increase per unit time

• no. of collisions per unit time with sufficient energy to overcome the Ea will increase

• No. of effective collisions will increase per unit time

• Rate of reaction increases

Collison theory for the nature of reactants

• Ionic compounds

• Organic reactions + molecules

• Metals

• Ionic compounds are usually faster than covalent compounds (since cov. bonds have to break and new ones are formed)

• Organic reactions are slow due to large covalent bonds. Molecules are large so eff. colli. lower

• Metals that are reducing agents(Mg Na) are faster than weaker reducing agents (Cu+Au)

When answering LCP questions you use SRFE+K what is it

• Identify the stress

• State how the system responds

• Which reaction is favored

• Effect after the new equilibrium is established ( what concentration for reactant/product increases or decreases)

• Is Kc constant or not

**** Differnce between enthalpy and change in enthalpy

• Enthalpy (H) is a thermodynamic property that represents the total heat content of a system at constant pressure. It accounts for both the internal energy of the system and the energy needed to push against the environment (like atmospheric pressure).

• Change in enthalpy (ΔH) is the difference in enthalpy between the reactants and products in a chemical reaction. It is often measured at constant pressure, and it corresponds to the heat absorbed or released by the system.