Factors That Affect the Chemical Reaction Rate

Factors That Affect the Chemical Reaction Rate Its useful to be able to predict whether an action will affect the rate at which a chemical reaction proceeds. Several factors can influence the chemical reaction rate. In general, a factor that increases the number of collisions between particles will increase the reaction rate and a factor that decreases the number of collisions between particles will decrease the chemical reaction rate. Concentration of Reactants A higher concentration of reactants leads to more effective collisions per unit time, which leads to an increased reaction rate (except for zero-order reactions.) Similarly, a higher concentration of products tends to be associated with a lower reaction rate. Use the partial pressure of reactants in a gaseous state as a measure of their concentration. Temperature Usually, an increase in temperature is accompanied by an increase in the reaction rate. Temperature is a measure of the kinetic energy of a system, so higher temperature implies higher average kinetic energy of molecules and more collisions per unit time. A general rule for most (not all) chemical reactions is that the rate at which the reaction proceeds will approximately double for each 10Â °C increase in temperature. Once the temperature reaches a certain point, some of the chemical species may be altered (e.g., denaturing of proteins) and the chemical reaction will slow or stop. Medium or State of Matter The rate of a chemical reaction depends on the medium in which the reaction occurs. It may make a difference whether a medium is aqueous or organic; polar or nonpolar; or liquid, solid, or gaseous. Reactions involving liquids and especially solids depend on the available surface area. For solids, the shape and size of the reactants make a big difference in the reaction rate. Presence of Catalysts and Competitors Catalysts (e.g., enzymes) lower the activation energy of a chemical reaction and increase the rate of a chemical reaction without being consumed in the process. Catalysts work by increasing the frequency of collisions between reactants, altering the orientation of reactants so that more collisions are effective, reducing intramolecular bonding within reactant molecules, or donating electron density to the reactants. The presence of a catalyst helps a reaction to proceed more quickly to equilibrium. Aside from catalysts, other chemical species can affect a reaction. The quantity of hydrogen ions (the pH of aqueous solutions) can alter a reaction rate. Other chemical species may compete for a reactant or alter orientation, bonding, electron density, etc., thereby decreasing the rate of a reaction. Pressure Increasing the pressure of a reaction improves the likelihood reactants will interact with each other, thus increasing the rate of the reaction. As you would expect, this factor is important for reactions involving gases, and not a significant factor with liquids and solids. Mixing Mixing reactants increases their ability to interact, thus increasing the rate of a chemical reaction. Summary of Factors The chart below is a summary of the main factors that influence the reaction rate. There is typically a maximum effect, after which changing a factor will have no effect or will slow a reaction. For example, increasing temperature past a certain point may denature reactants or cause them to undergo a completely different chemical reaction. Factor Affect on Reaction Rate temperature increasing temperature increases reaction rate pressure increasing pressure increases reaction rate concentration in a solution, increasing the amount of reactants increases the reaction rate state of matter gases react more readily than liquids, which react more readily than solids catalysts a catalyst lowers activation energy, increasing reaction rate mixing mixing reactants improves reaction rate

Anatomy of the Cerebellum and its Function

Anatomy of the Cerebellum and its Function In Latin, the word cerebellum means little brain. The cerebellum is the area of the hindbrain that controls movement coordination, balance, equilibrium and muscle tone. Like the cerebral cortex, the cerebellum is comprised of white matter and a thin, outer layer of densely folded gray matter. The folded outer layer of the cerebellum (cerebellar cortex) has smaller and more compact folds than those of the cerebral cortex. The cerebellum contains hundreds of millions of neurons for processing data. It relays information between body muscles and areas of the cerebral cortex that are involved in motor control. Cerebellum Lobes The cerebellum can be subdivided into three lobes that coordinate information received from the spinal cord and from different areas of the brain. The anterior lobe receives input primarily from the spinal cord. The posterior lobe receives input primarily from the brainstem and cerebral cortex. The flocculonodular lobe receives input from the cranial nuclei of the vestibular nerve. The vestibular nerve is a component of the vestibulocochlear cranial nerve. The transmission of nerve input and output signals from the cerebellum occurs through bundles of nerve fibers called cerebral peduncles. These nerve bundles run through the midbrain connecting the forebrain and hindbrain. Cerebellum Function The cerebellum is involved in several functions including: Fine movement coordinationBalance and equilibriumMuscle toneSense of body position The cerebellum processes information from the brain and peripheral nervous system for balance and body control. Activities such as walking, hitting a ball and playing a video game all involve the cerebellum. The cerebellum helps us to have fine motor control while inhibiting involuntary movement. It coordinates and interprets sensory information in order to produce fine motor movements. It also calculates and corrects informational discrepancies in order to produce the desired movement. Cerebellum Location Directionally, the cerebellum is situated at the base of the skull, above the brainstem and beneath the occipital lobes of the cerebral cortex. Cerebellum Damage Damage to the cerebellum may result in difficulty with motor control. Individuals may have problems maintaining balance, tremors, lack of muscle tone, speech difficulties, lack of control over eye movement, difficulty in standing upright, and an inability to perform accurate movements. The cerebellum may become damaged due to a number of factors. Toxins including alcohol, drugs, or heavy metals can cause damage to nerves in the cerebellum that lead to a condition called ataxia. Ataxia involves the loss of muscle control or coordination of movement. Damage to the cerebellum may also occur as a result of stroke, head injury, cancer, cerebral palsy, viral infection, or nervous system degenerative diseases. Divisions of the Brain: Hindbrain The cerebellum is included in the division of the brain called the hindbrain. The hindbrain is divided into two subregions called the metencephalon and myelencephalon. The cerebellum and pons are located in the upper region of the hindbrain known as the metencephalon. Sagittally, the pons is anterior to the cerebellum and relays sensory information between the cerebrum and cerebellum.