Since heat is released during the reaction, the product will have a lower energy than the reactant. You go from a higher energy level, as was the cse for "A" , to a lower energy level, as is the case for "B".
The difference in energy between "A" and "B" will the enthalpy change of the reaction, DeltaH. The difference between the activation energy of the forward reaction and the activation energy of the reverse reaction will be DeltaH.
You need to supply to "B" the exact amount of energy needed to g et it to go back to "A". More specifically, you need to provide it with the energy released during the forward reaction plus the energy needed to get the forward reaction going, i. Stefan V. Endothermic reactions are more common than exothermic reactions. The rates of exothermic reactions are faster than the rates of endothermic reactions.
Correct answer: None of these are valid answers. Explanation : The definition of an endothermic reaction is that the products have higher energy than the reactants, resulting in a positive enthalpy of reaction. Report an Error. Which of the following is an example of an exothermic reaction? Possible Answers: Water boiling. Correct answer: Magma cooling to form igneous rocks.
Explanation : In an exothermic reaction, heat has been released to the surroundings from the system. Possible Answers: Only endothermic reactions require energy in order to take place. Condensation of steam is an endothermic reaction. Endothermic reactions result in products with a lower internal energy.
Correct answer: Exothermic reactions have a lower activation energy compared to the reverse endothermic reactions. Explanation : When graphically tracking the energy of a reaction, you can see that energy is always needed to start a reaction, regardless of its enthalpy. The combustion of propane gas in a camping stove is an example of what type of reaction? Possible Answers: Exothermic reaction, with heat being absorbed.
Endothermic reaction, with heat being absorbed. Endothermic reaction, with heat being released. It depends on the temperature at which the reaction occurs. Correct answer: Exothermic reaction, with heat being released. Explanation : Combustion reactions occur when a compound is oxidized in a highly exothermic reaction. Which condition is always true for an exothermic reaction?
Possible Answers: There must be a catalyst involved. The molecular bonds of the compound are being broken. Correct answer: is negative. Explanation : When a reaction is exothermic "exo-" meaning out and "-thermic" having to do with heat , it means that the reaction is giving off heat into the environment.
Possible Answers: is positive. Copyright Notice. View Tutors. Matilda Certified Tutor. London Metropolitan University, Bachelors, Biochemistry. University of the Western Cape, Masters, Biotechnology.
Heat energy the total bond energy of reactants or products in a chemical reaction speeds up the motion of molecules, increasing the frequency and force with which they collide. It also moves atoms and bonds within the molecule slightly, helping them reach their transition state.
For this reason, heating up a system will cause chemical reactants within that system to react more frequently. Increasing the pressure on a system has the same effect. Once reactants have absorbed enough heat energy from their surroundings to reach the transition state, the reaction will proceed.
The activation energy of a particular reaction determines the rate at which it will proceed. The higher the activation energy, the slower the chemical reaction will be. The example of iron rusting illustrates an inherently slow reaction. This reaction occurs slowly over time because of its high E A. Additionally, the burning of many fuels, which is strongly exergonic, will take place at a negligible rate unless their activation energy is overcome by sufficient heat from a spark.
Once they begin to burn, however, the chemical reactions release enough heat to continue the burning process, supplying the activation energy for surrounding fuel molecules.
Like these reactions outside of cells, the activation energy for most cellular reactions is too high for heat energy to overcome at efficient rates. In other words, in order for important cellular reactions to occur at significant rates number of reactions per unit time , their activation energies must be lowered; this is referred to as catalysis. This is a very good thing as far as living cells are concerned. Important macromolecules, such as proteins, DNA, and RNA, store considerable energy, and their breakdown is exergonic.
If cellular temperatures alone provided enough heat energy for these exergonic reactions to overcome their activation barriers, the essential components of a cell would disintegrate. The Arrhenius equations relates the rate of a chemical reaction to the magnitude of the activation energy:. Collision theory provides a qualitative explanation of chemical reactions and the rates at which they occur, appealing to the principle that molecules must collide to react.
Collision Theory provides a qualitative explanation of chemical reactions and the rates at which they occur. A basic principal of collision theory is that, in order to react, molecules must collide. This fundamental rule guides any analysis of an ordinary reaction mechanism.
If the two molecules A and B are to react, they must come into contact with sufficient force so that chemical bonds break. We call such an encounter a collision. If both A and B are gases, the frequency of collisions between A and B will be proportional to the concentration of each gas. If we double the concentration of A, the frequency of A-B collisions will double, and doubling the concentration of B will have the same effect.
Therefore, according to collision theory, the rate at which molecules collide will have an impact on the overall reaction rate. Molecular collisions : The more molecules present, the more collisions will happen. When two billiard balls collide, they simply bounce off of one other. This is also the most likely outcome when two molecules, A and B, come into contact: they bounce off one another, completely unchanged and unaffected.
In order for a collision to be successful by resulting in a chemical reaction, A and B must collide with sufficient energy to break chemical bonds. This is because in any chemical reaction, chemical bonds in the reactants are broken, and new bonds in the products are formed.
Therefore, in order to effectively initiate a reaction, the reactants must be moving fast enough with enough kinetic energy so that they collide with sufficient force for bonds to break. This minimum energy with which molecules must be moving in order for a collision to result in a chemical reaction is known as the activation energy.
As we know from the kinetic theory of gases, the kinetic energy of a gas is directly proportional to temperature. As temperature increases, molecules gain energy and move faster and faster. Therefore, the greater the temperature, the higher the probability that molecules will be moving with the necessary activation energy for a reaction to occur upon collision. Even if two molecules collide with sufficient activation energy, there is no guarantee that the collision will be successful.
In fact, the collision theory says that not every collision is successful, even if molecules are moving with enough energy. The reason for this is because molecules also need to collide with the right orientation, so that the proper atoms line up with one another, and bonds can break and re-form in the necessary fashion.
For example, in the gas- phase reaction of dinitrogen oxide with nitric oxide, the oxygen end of N 2 O must hit the nitrogen end of NO; if either molecule is not lined up correctly, no reaction will occur upon their collision, regardless of how much energy they have.
However, because molecules in the liquid and gas phase are in constant, random motion, there is always the probability that two molecules will collide in just the right way for them to react. Of course, the more critical this orientational requirement is, like it is for larger or more complex molecules, the fewer collisions there will be that will be effective. An effective collision is defined as one in which molecules collide with sufficient energy and proper orientation, so that a reaction occurs.
According to the collision theory, the following criteria must be met in order for a chemical reaction to occur:. Collision theory explanation : Collision theory provides an explanation for how particles interact to cause a reaction and the formation of new products. The rate of a chemical reaction depends on factors that affect whether reactants can collide with sufficient energy for reaction to occur.
Explain how concentration, surface area, pressure, temperature, and the addition of catalysts affect reaction rate. Raising the concentrations of reactants makes the reaction happen at a faster rate.
For a chemical reaction to occur, there must be a certain number of molecules with energies equal to or greater than the activation energy. With an increase in concentration, the number of molecules with the minimum required energy will increase, and therefore the rate of the reaction will increase. For example, if one in a million particles has sufficient activation energy, then out of million particles, only will react.
However, if you have million of those particles within the same volume, then of them react. By doubling the concentration, the rate of reaction has doubled as well. Interactive: Concentration and Reaction Rate : In this model, two atoms can form a bond to make a molecule. Experiment with changing the concentration of the atoms in order to see how this affects the reaction rate the speed at which the reaction occurs.
In a reaction between a solid and a liquid, the surface area of the solid will ultimately impact how fast the reaction occurs.
This is because the liquid and the solid can bump into each other only at the liquid-solid interface, which is on the surface of the solid. The solid molecules trapped within the body of the solid cannot react. Therefore, increasing the surface area of the solid will expose more solid molecules to the liquid, which allows for a faster reaction.
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