7. Energy and Metabolism

Chemical Reactions

Introduction to Chemical Reactions and Equations | Don't Memorise

Chemical reactions introduction | Chemistry of life | Biology | Khan Academy

Science Shorts: What is a Chemical Reaction?

HCl &rarr; H+ + Cl-

 No. This reaction results in less complex products (greater entropy). Perhaps you remember the warning from chemistry about adding acid to water? 

C6H12O6 + 6 O2 &rarr; 6 CO2 + 6 H2O

 No. This represents the breakdown of glucose, a complex molecule, into less complex products (increasing entropy). 

ATP &rarr; ADP + Pi

 No. Remember that the hydrolysis of ATP is the source of most of the immediate energy for metabolism. 

 All of the listed responses are correct. 

 No. Only one of the choices is an endergonic reaction. 

glucose + fructose &rarr; sucrose

Keep in mind the relationship between the free energy change of a reaction and whether the reaction is spontaneous.

Which of the following reactions would be endergonic?

 The sign determines whether the reaction is spontaneous, and the magnitude determines the speed. 

No. Neither the sign nor the magnitude of &Delta;G has anything to do with the speed of a reaction.

The sign does not matter, but the larger the magnitude of &Delta;G, the faster the reaction.

The sign does not matter, but the smaller the magnitude of &Delta;G, the faster the reaction.

The more negative the &Delta;G, the faster the reaction is.

Neither the sign nor the magnitude of &Delta;G has anything to do with the speed of a reaction.

Does the equation for free energy include a way to indicate the speed of the reaction?

What do the sign and magnitude of the &Delta;G of a reaction tell us about the speed of the reaction? and

Animation: Exergonic and Endergonic Reactions

Types of Chemical Reactions

No. Entropy alone does not determine the change in free energy (&Delta;G).

No. The orderliness of a system is not related to the change in enthalpy (&Delta;H).

Orderliness relates to entropy.

If, during a process, the system becomes more ordered, then __________.

 They represent the way matter is created and destroyed. 

 No. Chemical reactions rearrange matter, but they cannot create or destroy matter under normal situations. 

 They reach chemical equilibrium when the amounts of products and reactants are equal. 

 No. Chemical equilibrium is reached when the forward and reverse reaction rates are equal. 

 They may have different numbers of a given atom on each side of the equation arrow. 

 No. The equation for a chemical reaction must always balance. 

 They involve the making and breaking of chemical bonds. 

Consider what is involved in chemical reactions and how we represent them.

Which statement is true about chemical reactions?

The traditional tree of life (shown above) presents the three domains as distinct, monophyletic lineages. However, other hypotheses propose different views on the relationships among the Archaea, Bacteria, and Eukarya. In particular, the two-domain hypothesis—or eocyte hypothesis—is emerging as a well-supported alternative to the three-domain hypothesis. The eocyte hypothesis, illustrated below, suggests that eukaryotes evolved from eocytes (also known as the Crenarchaeota—a major lineage of the Archaea). Resolving the relationships among these ancient lineages is difficult, but it has profound implications on our understanding of the origin of eukaryotic cells. <IMAGE>

Evaluate this statement: According to the two-domain hypothesis, all members of the domain Archaea are prokaryotes and therefore lack membrane-bound nuclei.

 No. Activation energy is required for both types of reactions. 

 the products are less complex than the reactants 

 No. The complexity of the products relative to the reactants is a measure of entropy, but increasing entropy is not the only thing that determines whether a reaction is exergonic. 

 activation energy exceeds net energy release 

 No. The amount of activation energy has nothing to do with whether a reaction is exergonic or endergonic. 

 No. An exergonic reaction releases free energy. 

 the potential energy of the products is less than the potential energy of the reactants 

Think about the differences in the characteristics of endergonic and exergonic reactions. and

A chemical reaction is designated as exergonic rather than endergonic when __________. and

Chemical Equations | Environmental Chemistry | Chemistry | FuseSchool

The traditional tree of life (shown above) presents the three domains as distinct, monophyletic lineages. However, other hypotheses propose different views on the relationships among the Archaea, Bacteria, and Eukarya. In particular, the two-domain hypothesis—or eocyte hypothesis—is emerging as a well-supported alternative to the three-domain hypothesis. The eocyte hypothesis, illustrated below, suggests that eukaryotes evolved from eocytes (also known as the Crenarchaeota—a major lineage of the Archaea). Resolving the relationships among these ancient lineages is difficult, but it has profound implications on our understanding of the origin of eukaryotic cells. <IMAGE>

Early ideas on the classification of life recognized all organisms as belonging to one of two fundamental lineages—prokaryotes or eukaryotes. Is this view compatible with either of the hypotheses illustrated here? Explain.

 The enzyme catalyzing the reaction’s having a high affinity (strength of binding) for the reactants 

No. What do you consider when calculating &Delta;G for a reaction?

 The enzyme catalyzing the reaction’s having a low affinity for the products 

No. The free energy of the products does influence &Delta;G of a reaction but does not determine the sign.

No. The free energy of the reactants does influence &Delta;G of a reaction but does not determine the sign.

 The free energy of the reactants and the free energy of the products 

Consider how you would calculate &Delta;G.

Which of the following determines the sign of &Delta;G for a reaction?

No. This reaction has a large increase in entropy, which in many cases will tend to make the &Delta;G for the reaction negative, meaning no energy input is needed.

No. The relative complexity of the reactants and products does not affect enthalpy (&Delta;H).

No. It is true that the change in disorder is associated with entropy (&Delta;S), but increasing disorder does not decrease entropy.

Consider how such a reaction relates to the orderliness of a system.

When one molecule is broken down into six component molecules, which of the following will always be true?

 occurs only when an enzyme or other catalyst is present 

 No. Spontaneous reactions can occur in the absence of a catalyst. 

 No. The occurrence of spontaneous reactions is not limited to living systems. 

 No. Anabolic pathways construct complex molecules out of simpler building blocks, and thus they require an input of energy (they are endergonic). 

 leads to a decrease in the entropy of the universe 

 No. Spontaneous reactions must increase the entropy of the universe according to the second law of thermodynamics. 

 releases energy when proceeding in the forward direction 

The word root exo means “outside.”

An exergonic (spontaneous) reaction is a chemical reaction that __________.

 No. Although the change in enthalpy does contribute to the spontaneity of a reaction, other factors must also be taken into account. 

 No. Although the change in entropy does contribute to the spontaneity of a reaction, other factors must also be taken into account. 

 All of these values reveal the direction in which a reaction will go. 

 No. Only one of the choices can determine definitively whether a reaction is spontaneous. 

Consider the energy dynamics of a spontaneous reaction.

Which part of the equation &Delta;G = &Delta;H &ndash; T&Delta;S tells you if a process is spontaneous?

 a decrease in the system's total energy will increase the probability of spontaneous change 

 No. This answer is true, but there is a better response. 

 increasing the entropy of a system will increase the probability of spontaneous change 

 increasing the temperature of a system will increase the probability of spontaneous change 

 a decrease in the system's total energy will increase the probability of spontaneous change, and increasing the entropy of a system will increase the probability of spontaneous change 

 a decrease in the system's total energy will increase the probability of spontaneous change, increasing the entropy of a system will increase the probability of spontaneous change, and increasing the temperature of a system will increase the probability of spontaneous change 

Recall the relationship between free energy, total energy, and entropy.

From the equation &Delta;G = &Delta;H &ndash; T&Delta;S it is clear that __________.

 The rate of the reverse reaction exceeds the rate of the forward reaction. 

 No. This would occur if additional products were added prior to the attainment of chemical equilibrium. 

 The forward and the reverse reactions have stopped. 

 No. The forward and reverse reactions do not stop and the relative concentrations of the reactants and products do not change when a reversible reaction is at chemical equilibrium. 

 The concentration of the reactants is equal to the concentration of the products. 

 No. Think about equal reaction rates, not equal concentrations of reactants and products. 

 The rate of the reverse reaction equals the rate of the forward reaction. 

Most chemical reactions are reversible, and chemical equilibrium is dynamic.

Which statement describes a reversible reaction that has reached chemical equilibrium?

What triggers a chemical reaction? - Kareem Jarrah

 A and B will be converted to C and D with a net release of energy. 

 No. Consider the relative amounts of free energy in the reactants and products. 

 The conversion of A and B to C and D is exergonic; the products are less organized than the reactants. 

 No. The products C and D contain more energy than the reactants, indicating this reaction is endergonic. Also, because the products contain more energy, they are more organized than the reactants. 

 The conversion of A and B to C and D is spontaneous. 

 No. Given that the products have more energy than the reactants, this reaction cannot occur spontaneously. 

 The entropy in the products, C and D, is higher than in the reactants, A and B. 

 No. The difference between the energies of the reactants and products is a positive number; therefore, the process is endergonic, and the products are more organized. Thus, the products have lower entropy than the reactants. 

 The reaction that proceeds to convert A and B to C and D is endergonic; the products are more organized than the reactants. 

Keep in mind the relationship between the free energy change of a reaction and what that means about the nature of the reaction.

Molecules A and B contain 110 kcal/mol of free energy, and molecules B and C contain 150 kcal/mol of energy. A and B are converted to C and D. What can be concluded?

The products have more total energy than the reactants.

The reaction proceeds with a net loss of free energy.

The reaction goes only in a forward direction: all reactants will be converted to products.

A net input of energy from the surroundings is required for the reactions to proceed.

Which of the following statements is true for all exergonic reactions?a) The products have more total energy than the reactants.b) The reaction proceeds with a net loss of free energy.c) The reaction goes only in a forward direction: all reactants will be converted to products.d) A net input of energy from the surroundings is required for the reactions to proceed.

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