B2 Chapter 11 Q2 Flashcards
(23 cards)
What is meant by a ‘species’ in chemistry?
A species is any chemical entity involved in a reaction, such as an atom, ion, or molecule. It can also refer to intermediates and products. Understanding which species are present helps describe the full course of the reaction.
What is a reaction mixture?
A reaction mixture includes all substances present during a chemical reaction—reactants, products, and catalysts. Its composition changes over time as the reaction progresses. Analyzing it helps track reaction progress or identify when equilibrium is reached.
What is a reaction vessel and why is it important?
A reaction vessel is the container in which a chemical reaction occurs. It must be suitable for the reaction conditions, such as temperature or pressure. Choosing the right vessel ensures safety and reliable results.
How is colour intensity related to chemical reactions?
Colour intensity refers to how strong or deep the colour of a solution appears. It’s often linked to the concentration of coloured species in the solution. Measuring changes in colour intensity can be used to monitor reaction progress using a colorimeter.
What is chirality in chemistry and why is it important?
Chirality describes molecules that are mirror images but not superimposable, like left and right hands. These molecules often have a carbon atom bonded to four different groups, called a chiral centre. Chiral molecules exist as enantiomers, which can have very different biological effects. For example, one enantiomer of thalidomide is therapeutic, while the other caused birth defects.
What is refractive index and how is it used in chemistry?
The refractive index is the ratio of the speed of light in a vacuum to its speed in a material. It shows how much light bends when it enters a substance. This property helps identify substances or measure concentration, especially in liquids like sugar solutions. A higher concentration usually means a higher refractive index.
What does it mean for two quantities to be proportional?
Two quantities are proportional if they increase or decrease in the same ratio. For example, if one doubles, the other also doubles. In chemistry, rate is often proportional to concentration, meaning rate ∝ [A]. Proportionality helps predict how changing one variable affects another.
What is concentration and why is it important in reactions?
Concentration is the amount of a substance in a certain volume, usually measured in mol dm⁻³. It affects how often particles collide and react. Higher concentration usually leads to faster reactions because more particles are available to collide. For instance, a more concentrated acid reacts faster with metals.
What does ‘rate’ mean in the context of chemical reactions?
Rate refers to how fast a chemical reaction happens. It’s usually measured by how quickly a reactant is used up or a product forms, often in mol dm⁻³ per second. Factors like temperature, concentration, and catalysts can change the rate. For example, combustion reactions happen much faster than rusting.
What is a mathematical relationship in reaction kinetics?
A mathematical relationship shows how variables are connected, often through an equation. In kinetics, the rate equation links the reaction rate to the concentration of reactants. For example, rate = k[A]² means the rate is proportional to the square of A’s concentration. This helps predict how changing [A] affects the rate.
What is a second order rate equation and how does it work?
A second order rate equation means the rate depends on either the square of one reactant’s concentration or the product of two different concentrations. It can be written as rate = k[A]² or rate = k[A][B]. If [A] doubles in the first case, the rate increases by four times. This usually involves two particles colliding in one step.
What is a zero order rate equation and what does it tell us?
A zero order rate equation means the reaction rate does not depend on the concentration of any reactant. It’s written as rate = k, where k is constant. This means changing the concentration doesn’t change the rate. Such reactions often occur when a surface catalyst is saturated or an enzyme is fully active.
Why doesn’t concentration affect the rate in a zero order reaction?
In a zero order reaction, the rate is limited by a factor other than concentration, such as a saturated catalyst surface. All active sites are already full, so adding more reactant won’t increase the reaction speed. The rate stays constant until the concentration drops and active sites become available again. A good example is when a solid catalyst surface is fully covered.
What is a stoichiometric equation and why is it important?
A stoichiometric equation is a balanced chemical equation showing the exact mole ratios of reactants and products. It follows the law of conservation of mass, meaning atoms are balanced on both sides. These equations help us calculate how much of each substance is needed or produced. For example, 2H₂ + O₂ → 2H₂O shows the ratio 2:1 for hydrogen to oxygen.
What does ‘stoichiometric’ mean in chemistry?
‘Stoichiometric’ refers to the exact proportions of substances needed for a complete reaction, with no excess. It comes directly from the balanced chemical equation. Using stoichiometric amounts ensures the most efficient use of reactants. For example, 1 mole of O₂ reacts perfectly with 2 moles of H₂ to make water.
Why must particles collide with the right geometry in a chemical reaction?
Particles must align properly when they collide to form new bonds and start a reaction. If they collide at the wrong angle, even with enough energy, no reaction occurs. This is called having the correct “collision geometry”. For example, in the hydrogen and iodine reaction, atoms must face the right way to react. Geometry affects the number of successful collisions.
What are experimental methods in chemistry and what are they used for?
Experimental methods are procedures used to study chemical reactions and measure things like concentration, rate, and composition. These include titration, spectroscopy, and colorimetry. They help chemists gather accurate data during experiments. For example, using a colorimeter can track how quickly a solution changes colour over time.
What is the rate-determining step in a reaction?
The rate-determining step is the slowest step in a reaction mechanism. It controls the overall reaction speed, like a bottleneck in a process. The rate law often matches the molecularity of this step. For example, if only one molecule is involved in this step, the reaction is likely first order. Understanding it helps in predicting how changes affect the rate.
What is an intermediate in a chemical reaction?
An intermediate is a temporary substance formed during a reaction but not shown in the final balanced equation. It’s made in one step and used in another, so it doesn’t appear in the overall reaction. Intermediates are usually short-lived and unstable. For example, nitrogen dioxide acts as an intermediate in some nitrogen monoxide reactions.
What does ‘medium’ mean in a chemical context?
In chemistry, the medium is the environment where a reaction happens, like a solvent or the physical state (solid, liquid, or gas). The medium can affect how fast and how well a reaction occurs. For instance, a reaction may go faster in water than in ethanol, or behave differently in gas than in solution. Choosing the right medium helps control the reaction.
What does it mean to withdraw something during a chemical experiment?
To withdraw means to take something out of a system, like removing a small amount of liquid during a reaction. Chemists often withdraw samples to check progress, measure concentration, or do tests. For example, during titration, a chemist might withdraw a sample to test with an indicator. It’s a way to monitor reactions without stopping them.
What is the instantaneous reaction rate?
The instantaneous rate is the speed of a reaction at one exact moment in time. It’s found by taking the gradient (slope) of a concentration–time graph at a single point. At the start, the rate is usually higher because reactants are most concentrated. As reactants get used up, the instantaneous rate becomes lower. This is different from average rate, which is over a time period.
Why is rate sometimes plotted as 1/T in rate-concentration graphs?
In some graphs, rate is shown as 1/T because rate and time are inversely related. T is the time taken for a reaction step, like a half-life. If the time is short, the reaction is fast, so 1/T is high. Plotting 1/T helps show how concentration affects rate, especially in first order reactions. It makes it easier to compare how fast reactions happen at different concentrations.
