Activation energy can be either positive or negative, but what does that really mean? Oftentimes, when we hear the term ‘activation energy,’ it is in reference to how much effort it takes for a chemical reaction to occur. This article will discuss whether or not activation energy can be negative and more importantly, what this means for a chemical reaction.
When looking at the law of thermodynamics, you’ll see that there are certain things that require an input of work before they can happen (such as heating up water). In other words: “work” has been done to get them ready so their bonds can break apart and create new ones with other molecules. It would stand to reason then that if these reactions have some sort of activation energy, it would be positive.
However, there are some reactions that can occur spontaneously without the need for an input of work or activation energy (such as rusting metals). This is what’s known as a spontaneous reaction and has negative activation energy. These types of reactions will happen more quickly than ones with high levels of activation energy because they require less effort to get started. So then: could reactants have different amounts of activation energies? Yes! It all depends on how well-developed their bonds are in order to break them apart so new bonds can form with other molecules.”
Positive Activation Energy: The amount required to make chemical changes take place; must exceed the natural level at which substances exist
Work: An input of energy that is needed for certain reactions to happen. This can come in a large variety including physical, electrical, and heat. Larger inputs are usually called work while smaller ones are often referred to as activation energy.
Reactant: Molecules or atoms that combine during a reaction with other reactants or even themselves
Chemical Change: A change involving both matter and energy where bonds between molecules break apart and new bonds form with different molecules (this can involve many types of bonding)
Natural Level: How much something naturally happens without any outside influence happening upon it- this could include things like the speed at which a reaction can happen
Sequester: Isolate or remove from interaction with other things. An example of this is when water is removed from an electrolytic cell in order to prevent it from interfering with what’s happening inside.
Thermodynamics: The branch of physics that studies energy and its transformations, such as heat flow- especially by conduction, convection, and radiation
Reaction Quotient (Q): A math equation used for determining equilibrium concentrations of reactants based on their stoichiometry
Equilibrium Constant (K): Another name for Q; also equal to -RTln(Q) where R = 0.08206 ln((P/T)/0), T= temperature K , and P = pressure
Electrolytic Cell: A cell that creates current by using electricity to break down chemicals into ions for a charge.
Arrhenius Equation: An equation used in thermodynamics to calculate the activation energy of a chemical reaction based on temperature
Potential Difference (PD): Electrical potential difference between two points in an electric circuit
Electrochemical Cell: A cell that creates current by using electricity to break down chemicals into ions for a charge.
Activation Energy (E): The minimum amount of energy needed in order for an electrochemical or any other type of chemical reaction make take place- it can be positive, negative, or zero at times; its calculated as being equal to -RTln(Q) where R= 0.08206 ln((P/T)/0) T=temperature K, and P is pressure Potential Difference (PD): Electrical potential difference between two points in an electric circuit
Positive Charge: A particle that has more protons than electrons and is therefore positively charged; can be found in the nucleus of an atom.
Negative Charge: The opposite of a positive charge- it occurs when there are more electrons than what’s required for neutrality, meaning they have fewer portions and therefore have negative charges
Charge Density (Q): Amount or concentration of electric charge within a region on a conductor surface “A(delta) Q” = change in electrical potential with respect to distance from some point (r), measured at two different points separated by a small length ds between them. Charges closer together will attract each other while those further apart will repel one another
Potential Difference Across An Insulator: The potential difference between two points on an insulator is the work per unit charge that would be necessary to move a test charge across each point
Current Density (I): Amount of electric current passing through a surface area in some time interval, usually measured in amperes per square meter. This can also be called ‘concentration’