6.4 Chemical Reactions Flashcards Preview

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Flashcards in 6.4 Chemical Reactions Deck (45)

what is a chemical reaction?

the process by which molecules, called reactants, are transformed into other molecules, called products


what changes during a chemical reaction?

the bonds linking the atoms


most chemical reactions in the cell are readily reversible, what does that mean?

the products can react to form the reactants


the way the reaction is written defines forward and reverse reactions:

a forward reaction proceeds from left to right, a reverse reaction proceeds from right to left


the direction of a reaction can be influenced by:

the concentrations of reactants and products


how to favour the forward reaction?

increase the concentration of the reactants or decrease the concentration of the products


the effect of favouring the forward reaction can be found in the reactions of many metabolic pathways, how does that work?

the products of many reactions are quickly consumed by the next reaction, helping to drive the first reaction forward


Gibbs free energy (G)

the amount of energy available to do work


how does one determine whether the reaction releases energy that is available to do work?

you can compare the free energy of the reactants and products


what is delta G (change in G)

the free energy of the products minus the free energy of the reactants


if change in G is positive:

the products of a reaction have more free energy than reactants and a net input of energy is required to drive the reaction forward


if change in G is negative:

the products of a reaction have less energy than reactants and energy is released and available to do work



describes reactions with a negative change in G that release energy and proceed spontaneously



describes reactions with a positive change in G that are not spontaneous and so require an input of energy


spontaneous in the context of free energy means that:

a reaction releases energy


non-spontaneous in the context of free energy means that:

a reaction requires a sustained input of energy


the total amount of energy is equal to:

the energy available to do work plus the energy that is not available to do work because of the increase in entropy


enthalpy (H)

the total amount of energy in a system


entropy (S)

the degree of disorder in a system


absolute temperature (T)

temperature measured on the kelvin scale


the formula for the total amount of energy (H) is:

energy available to do work (G) + energy lost to entropy (TS)


the formula to determine energy available to do work (G) is:

H - TS
total amount of energy - energy lost to entropy


the value of change in G depends on BOTH the:

change in enthalpy and the change in disorder


catabolic reactions are those in which the products have :

less chemical energy (lower enthalpy) in their bonds than reactants have, the products are more disordered (higher entropy) than the reactants are-have a negative value of change in H and a positive value for change in S (releases energy-spontaneous)


anabolic reactions are the opposite of catabolic reactions so:

increasing chemical energy (positive delta H) and decreasing disorder (negative delta S0, synthesis of macromolecules, positive value of delta G, requires a net input of energy


if the change in enthalpy and entropy are both positive or both negative, whether or not the reaction is spontaneous is determined by:

the absolute value of these parameters which then determines whether delta G is positive or negative


what effect does increasing temperature have on the free energy (delta G) of a chemical reaction?

increasing the temperature increases the value of (TS) which decrease G (G=H-TS)


hydrolysis reactions consist of a chemical reaction in which a water molecule is split into:

a proton (H+) and a hydroxyl group (OH-), hydrolysis reactions often break down polymers into their subunits and in the process one product gains a proton and the other gains a hydroxyl group


the reaction of ATP with water is an exergonic reaction because:

there is less free energy in the products compared to the reactants


why is the reaction of ATP an exergonic reaction?

ADP is more stable than ATP, contains less chemical energy in its bonds (negative H), and because there is two molecules (ADP and P), there is increased entropy (H), so G is negative and the reaction is spontaneous and releases energy


the free energy difference for ATP hydrolysis is approximately: (under lab conditions)

-7.3 kcal per mole of ATP


the value of the free energy difference for ATP hydrolysis is influenced by several factors including:

the concentration of reactants and products, the pH of the solution, and the temperature and pressure


in cell conditions, the free energy difference is approximately:

-12 kcal per mole of ATP


the release of free energy during ATP hydrolysis comes from:

breaking weaker bonds (with more chemical energy) in the reactants and forming more stable bonds (with less chemical energy in the products)


the change in G for the forward and reverse reactions have the same:

absolute value but opposite signs


energetic coupling

the driving of a non-spontaneous reaction by a spontaneous reaction


energetic coupling requires that the net change in G of the two reactions be:

negative and the two reactions must occur together or share an intermediate


the synthesis of ATP from ADP and inorganic P is an:

endergonic reaction with a positive change in G requiring an input of energy


in some cases, the synthesis of ATP can be driven by:

exergonic reactions through energetic coupling


hydrolysis reactions can be ranked by:

their free energy differences (change in G)


ADP is an energy:



ATP is an energy:



reactions with a free energy difference more negative than that of ATP hydrolysis transfer:

a phosphate group to ADP by energetic coupling (helping to drive ATP synthesis because it is more exergonic)


reactions with a free energy differences less negative than that of ATP hydrolysis receive:

a phosphate group from ATP by energetic coupling (because it is less exergonic compared to ATP hydrolysis)


the free energy difference for ATP hydrolysis compared to hydrolysis of common phosphorylated molecules is:

intermediate which allows ATP to drive reactions as well as be replenished