Reaction rate and equiliberium Flashcards
Energy
Capacity to do work or cause change measured in joules
Law of conservation of energy
All forms of energy , heat,electrical,light,chemicals, potential and kinetic are interchangeable, however the total amount of energy present is always constant.
Meaning whenever one form of energy reduces in amount then another form of energy will increase in amount so that the total quantity of energy present is unchanged. Thus if the energy present in a given system falls then there will be a corresponding rise in the energy of its surroundings so that the total energy in the system plus surroundings remains constant.
Energy changes
During chemical change, energy in the form of heat, light or electrical energy can be produced or consumed. Sometimes for example the surroundings of a reacting system is seen to heat or cool simply because of the chemical reaction is taking place. These heating or cooling results from a difference in enthalpy of the products of the reaction compared to what was originally present in the reactants.
Enthalpy
Enthalpy is the measure of the energy present in a substance it includes but is not limited to the energy stored in chemical bonds known as chemical potential energy and particle kinetic energy.
Weak bonds hold more chemical potential energy then strong bonds
What happens in a chemical change
Some bonds are broken and new ones are formed and so there will inevitably be a change ( increase or decrease) in the amount of stored chemical potential energy. As energy must be conserved, any change in chemical potential energy must be balanced by an opposite change in some other form of energy usually particle kinetic energy (heat). This means the temperature of a reaction system will rise or fall and cause heat energy to flow into and out of the reaction system
This flow of heat into or out of a reacting system changes the enthalpy total energy of the reacting system.
Exothermic reactions
Reactions that lose heat to surroundings
Negative value for delta H
Enthalpy decreases during this course of reaction
Some of the chemical potential energy stored in bonds is converted to particle kinetic energy, this cause increase in systems tempreture and overall energy is conserved with chemical Potential energy becoming heat energy however as this changes raises the reacting systems tempreture heat then flows out form the hot system to the cooler surroundings . The loss of heat energy from the systems to the surroundings mean that the system’s enthalpy total energy has reduced and delta h is negative
Endothermic
Reactions that gain heat from surroundings
Have positive value for delta H
Enthalpy increases during course of the reaction. This will happen if some of the particle kinetic energy in the reacting system is converted to chemical potential energy stored in bonds overall there is no change in enthalpy initially however as a consequence of the reduced particle kinetic energy the reacting system temp will fall and heat then flows form the warmer surrounding to the cooler reacting system.
This now increases the reacting system’s total energy,ie its enthalpy hence delta H is positive
Chemical reaction rate
Measure of the rate at which reactants are consumed and products are formed.
What does the rate of chemical reactions increase with ?
Temperature
Concentration
Pressure
State of sub-division
Catalyst
What is a catalyst ?
Unique substances which are involved in a reaction mixture to increase rate without apppearing to be consumed by the reaction.
Amount of catalyst present in a reaction mixture does not change as the reaction proceeds
How can the way in which reactions occur and why these conditions affect the rate be explained by collision theory
The theory describes chemical reactions in term of individual particle collisions.
According to collision theory for a reaction to occur what following conditions must be met
The reacting particles : atoms, molecules or ions must collide
The collision energy must equal or exceed a certain minimum amount known as the activation energy
The reacting particles must collide with a suitable orientation
How does concentration effect rate of reaction ?
Raising of an aqueous regent increase reaction rate
The higher the concentration of reacting particles cause an increase in the rate of collisions between these particles this greater rate of collisions is the reason for the observed increase in reaction rate.
How does gas pressure increase rate of reaction ?
Raising the pressure, by reducing the volume or adding more gas to the same container creates a greater concentration of reacting gas molecules, hence an increase in the rate of reaction typically doubling the pressure of gaseous regent will double the reaction rate
How does increase in temperature of a reaction mixture increase the reaction rate
At a higher tempreture, particles on a average have a greater kinetic energy energy as tempreture is the measure of a average kinetic energy Ek= 1/2mv squared the particles of a substance. As the tempreture of a substance rises so does the avaerge kinetic energy of its particles. Thus at a higher temp the average collision energy of the reacting particles in reaction mixture increases and a greater percentage of collisions will have a sufficient energy Activation energy to form activated complex thus a greater percentage of collisions are successful and hence reactation rate increase with increasing tempreture.
