Rates of Reaction (Edexcel IGCSE Science (Double Award): Chemistry): Flashcards

Increasing concentration means more reactant particles are present in a given volume, so collisions occur more frequently and the number of successful collisions per second increases.

False.

Increasing temperature increases both the frequency of collisions and the kinetic energy of particles, so more collisions have energy greater than the activation energy and are therefore successful. Both effects contribute to a faster rate.

Increasing the pressure of a gas has the same effect as increasing the concentration of a solution, because the same number of particles are forced into a smaller volume.

Decreasing particle size increases the surface area of the solid reactant, exposing more particles to the other reactant and increasing the frequency of collisions per second.

True.

A higher concentration means more particles in the same volume, so there are more frequent collisions per unit time. This increases the rate of reaction.

As a rough guide, for every 10 °C increase in temperature, the rate of reaction in aqueous and gaseous systems approximately doubles. This is a useful approximation, not an exact rule.

A successful collision is a collision between reactant particles in which the particles have sufficient energy to overcome the activation energy and form products.

A small rise in temperature gives particles more kinetic energy, so they move faster and collide more frequently. More importantly, a greater number of collisions have energy equal to or greater than the activation energy, making them successful. This means the rate increases significantly.

A catalyst is a substance that increases the rate of reaction without itself being chemically altered or consumed at the end of the reaction.

A catalyst provides an alternative reaction pathway that has a lower activation energy. This means more collisions are successful, so the rate of reaction increases.

False.

A catalyst is chemically unchanged at the end of the reaction, so its mass at the start and end of the reaction is the same.

A catalyst increases the rate of reaction by providing an alternative pathway with a lower activation energy, meaning more particles have sufficient energy to react.

Catalysts increase the rate of reaction and therefore the rate of production, and they reduce energy costs because reactions can be run at lower temperatures.

True.

Different chemical reactions have different activation energies and mechanisms, so a specific catalyst is needed to provide the appropriate alternative pathway for each reaction.

Only small amounts of a catalyst are typically needed to have a significant effect on the rate of reaction.

Enzymes act as catalysts in biological systems, increasing the rates of biochemical reactions without themselves being consumed.

Marble chips are pieces of calcium carbonate (CaCO₃) used as the solid reactant in the surface area investigation, reacting with dilute hydrochloric acid to produce carbon dioxide gas.

Carbon dioxide gas is produced when marble chips (calcium carbonate) react with dilute hydrochloric acid.

In the surface area experiment, the volume of carbon dioxide produced is measured by collecting gas in an inverted measuring cylinder filled with water.

True.

Powdered marble chips have a greater surface area, exposing more particles to the acid, which increases the frequency of successful collisions and therefore increases the rate of reaction.

The volume and concentration of hydrochloric acid and the mass of the solid must be kept constant so that surface area is the only independent variable being changed.

Increasing the surface area of marble chips increases the rate of reaction because more surface particles are exposed to the acid, increasing the number of successful collisions per second.

False.

The total amount of product depends on the amount of reactants used, not their particle size. Smaller chips react faster but produce the same total volume of gas.

An inverted measuring cylinder filled with water and submerged in a water trough collects the gas by downward displacement of water, allowing the volume of gas produced to be read directly. Both methods are valid. The cylinder is simple and widely available.

Hydrogen peroxide solution (H₂O₂) is the reactant that undergoes catalytic decomposition in this practical.

Oxygen gas is produced when hydrogen peroxide decomposes, and its volume is collected and measured using an inverted measuring cylinder.

In the catalyst practical, the volume of gas produced in a fixed time is measured and compared for different catalysts to determine which is most effective.

False.

Several solids can act as catalysts for this reaction, including lead(II) oxide, iron(III) oxide and copper(II) oxide as well as manganese(IV) oxide.

The volume of gas produced in a fixed time is measured for each catalyst and results are plotted on the same graph, so the relative rates of decomposition can be directly compared.

The catalyst is added to the conical flask containing hydrogen peroxide and the bung is closed, the gas produced travels through a delivery tube into an inverted measuring cylinder.

False.

A catalyst is chemically unchanged at the end of the reaction, so its mass remains the same before and after the reaction.

The volume of hydrogen peroxide must be kept constant so that the amount of reactant is the same in each trial, making the comparison of different catalysts a fair test.