Bigger is not always better

TO INVESTIGATE THE CAUSE OF REACTION RATE DIFFERENCE

Thermodynamics - Interaction Studies - Solids, Liquids and Gases, 2011

2020

The temperature-size rule (TSR) describes the inverse relationship between organism size and environmental temperature in uni- and multicellular species. Despite the TSR being widespread, understanding the mechanisms for size responses to environmental warming remain elusive. Here, we experimentally test three hypotheses (differential development and growth [DDG], maintain aerobic scope and regulate oxygen supply [MASROS] and the supply-demand hypothesis [SD]) explaining the TSR using the aquatic protist Colpidium striatum in three gradually changing and a constant temperatures crossed with three different nutrient levels. We find the constant and slowly warming environments show similar responses in terms of population dynamics, whereas the linear and fast populations quickly decline and also show a stronger temperature-size reponse. Our analyses suggest that acclimation may have played a role in observing these differences among treatments. Further analyses reveal that the SD hypo...

Journal of Education and Vocational Research, 2015

An object when heated will undergo expansion. Expansion of an object is affected by the expansion coefficient, temperature, and type of object substances that cause the length, area, and volume of the object and other objects differently. Based on these concepts, to investigate the comparative increase in the size of the object that is affected by factors that affect the expansion by heating the body until it reaches the equilibrium temperature. As the object under study will use a block of copper and water with each volume to be measured 10-5 m3 added volume ratio. With the initial temperature of each object 20 oC, both substances will be heated up to a temperature of 30oC, 35oC, 40oC, 45oC, dan 50oC. Both substances are then calculated and compared to the increase in volume experimentally and theoretically. After calculation, a score which indicates that the copper block and the water volume is different. Increase the volume of water is greater than the increase in the volume of c...

There is much information that can be derived from a chemical equation: for example, the products that can be expected from a given set of reactants and the stoicbiometric relationship between the substances involved in the reaction (1). The equation, however, does not reveal anything about the conditions under which the reaction will take place, its efficiency, or the "rate" at which the reaction occurs. By rate is meant the number of chemical changes which take place on n molecular scale per unit of time (2). .~-~~ ~ ~ By examination of numerous chemical reactions, one observes that certain types of chemical reactions proceed faster than others. For example, the explosion of nitroglycerine proceeds rapidly, while the rusting of iron generally occurs so slowly that it is scarcely perceptible. Some reactions go essentially to completion (little or no reactant remains), whereas others are in a state of dynamic equilibrium, a situation in which reactanb form products a t the same rate that products are transformed into reactants. In chemical reactions, rates are usually measured in terms of how fast products appear or how fast reactants disappear. Color, pressure, concentration, and mass changes are some parameters that are frequently used to monitor a reaction's propress. ~~ Reaction rates and reaction efficiency are of great importance to the chemist: often the practicability of a chemical ~ ~ reaction, particularl$ a commeriial process, depends on the reaction's rate and efficiency. If the reaction is too slow or the equilibrium is not shifted in favor of the products, it may not be economically feasible. The study of chemical equilibrium deals only with the limit or extent to which a reaction can occur; it is only concerned with the initial and final states of the chemical system. Chemical kinetics, however, is concerned with the reaction mechanism, i.e., the sequence of steps by which a chemical reaction proceeds, the rates of these steps, and the factors, like nature of reactants, concentration, temperature, and catalysis, which affect the rate. The Colllslon Theory of Reaction Rates A concept, known as the collision theory, has been developed to explain why certain factors, such as the nature of reactants, concentration, and temperature, affect the rare of a chemical reaction. This theory is based on the idea that for n reaction to occur. there must he collisions between reactant particles. ~c c o r d i "~l~, the rate of reaction depends upon the number of collisions per unit of time and the fraction of these collisions that are effectiue. By effectiue collisions is meant interoarticle contacts between reactants that are successful in the formation of products. Nature of Reactants Substances differ in activitv and hence in the rate with which they react with other substances. For example, an actlve metal like ootassium will displace hydrogen vigorously and rapidly from acids, while lessactive metals, like lead or platinum , react very slowly, if a t all as in the case of platinum. A more detailed discussion of the relative activities of metals can be found in an earlier article in this series (3). Another factor to be considered is that a chemical reaction is a process in which existing honds are broken and new honds are formed. Therefore, the reaction rate will depend on the specific honds involved and hence on the nature of the reac-tant. As a result, one should expect to find that reaction rates vary greatly with changes in molecular structure. This can he seen by comparing the rate of reaction of iron(I1) and per-manganate ions with that of oxalic acid molecules and per-manganate 2MnOa-I,,) + 10Fe(.,12+ + 16H(.,)+ (purple)-2Mn(JC + 10Fe(,13+ + 8H&) s (pink) E 2Mn041.d + + 6 H w t F (purple)-~MII(,)~+ + 10C02(,l + 8H,O(t, (pink) In both cases the purple permanganate disappears as the pink manganese(I1) ion appears; however, in the first reaction the purple color disappears almost instantaneously upon addition of a stoichiometric quantity of iron(I1) indicating that the reaction occurs very rapidly. On the other hand, the disappearance of the purple color in the second reaction requires a much longer period of time; therefore, the reaction must occur more slowlv. Even at elevated temperatures the second reaction is slow unless catalyzed by ma&nese(11) ion. (This is an example of autocatalysis, i.e., Mn2+, a reaction product, serves to catalyze its own formation.) Everything is identical in these two reactions except for the nature of one of the reactants; iron(I1) is an ion whereas oxalic acid is a molecule. Generallv, ionic reactants are found to yield products a t a much faker rate than covalent molecules. Two reasons can be suggested for the observed difference in rate of reaction. First. the Dermaneanate and iron(I1) are hoth ions. Reactions occurring hetween ions of opposite charge H and essentiallv spherical charpe distribution are usually rapid ,. . because effective interparticle contact can occur from any relative direction of approach. That is, the influence of moM . . lecular size and geometry (4) on reaction rate, commonly re-I ferred to as the "steric" effect, is minimal in ionic reac-J tions. The second reason concerns the probability that properly T oriented oxalic acid molecules will collide with properly ori-R ented permanganate ions. The probability of a permanganate ion colliding with a nonreactive part of the molecule is considerably greater for the oxalic acid molecule than for the iron(I1) ion. Consequently, the rate of effective collision, and the rate of overall reaction, should he slower for the oxalic acid than for the iron(I1) ion. Concentration of Reactants From a kinetic standpoint, chemical change takes place as a result of molecular collisions. The ereater the numher of ~ ~ collisions per unit of time, the greaterihe probahility of conversion of reactants into oroducts Der unit of time, i.e., the greater the rate of reaction. By increasing the concentration of any or all of the reactants, each molecule has a greater probability of colliding with another molecule and partici-natine in a reaction.-Tu develop the quantitative notions of reaction rate, consider the reaction between raseous iodine and hromine to form gaseous iodine monohrom~de +