6 1 rate of reaction

The rate of reaction is a measure of how fast a reactant is used up or how fast a product is made.

Three techniques used in a lab that are used to measure the rate of a reaction include:

The equation for calculating rate of reaction in terms of reactants is: Rate = amount of reactant used / time taken

The equation for calculating rate of reaction in terms of products is: Rate = amount of product made / time taken

The mass loss method is a technique for determining reaction rate by measuring the decrease in mass of the reaction vessel, over time, as a gas escapes.

The gas collection method is a technique for determining reaction rate by measuring the volume of gas produced over time.

The precipitation method is a technique for determining reaction rate by measuring the time it takes for a precipitate to form and obscure a cross drawn under the reaction vessel.

True. The units for rate of reaction always include time in the denominator.

Disadvantages of measuring the rate of a reaction by collecting gas in an inverted measuring cylinder include:

Disadvantages of measuring the rate of a reaction by collecting gas using a gas syringe include:

An advantage of measuring the rate of a reaction via the formation of a precipitate is that no specialist equipment is needed.

The typical units for expressing rate of reaction in terms of moles are moles per second, mol/s.

To convert mass per unit time to moles per unit time, divide the mass per unit time by the molar mass of the substance.

The molar gas volume is 24,000 cm3/mol.

To convert volume per unit time to moles per unit time for gases, divide the volume per unit time by the molar gas volume (24,000 cm3/mol).

False. There is no direct way to measure moles, so it is necessary to calculate the rate using mass or volume first.

The equation for converting mass to moles is: moles = mass / Mr

The first step in calculating rate of reaction in mol/s when given time in minutes is to convert minutes to seconds.

True. The molar gas volume is the same for all gases at room temperature and pressure.

Line A shows magnesium powder reacting with acid and line B shows magnesium ribbon reacting with acid.

The reactions takes 30 seconds to complete. The point at which the line plateaus is when the reaction is complete.

Line A is magnesium reacting with concentrated acid, and line B is magnesium reacting with dilute acid.

The reaction is the fastest at the beginning of a reaction. Between 0 and 10 seconds.

True. The gradient of the line in a rates graph is equal to the initial rate of reaction.

False. The steeper the gradient of the line in a rates graph then the faster the rate of reaction.

A horizontal line in a rate graph indicates that the reaction has finished.

The line on the graph that represents the reaction that takes place at a higher temperature is A.

The line on the graph that represents the reaction that takes place with a catalyst is A.

The lines on the graph that indicate a reaction that has taken place between acid and

To calculate the gradient at a specific point on a curved graph:

False. The gradient varies at different points along a curved rate graph.

The gradient represents the rate of reaction at a specific point in time.

True. A steeper tangent indicates a faster rate of reaction at that point.

You can compare rates of reaction at different points on a curved graph by calculating and comparing the gradients of tangents at those points.

The equation for calculating gradient is: gradient = change in y / change in x

The five factors that can affect the rate of a reaction are:

Magnesium powder has a greater surface area.

Increasing the concentration will increase the rate of reaction.

False. Adding a catalyst to a reaction will increase the rate.

Decreasing temperature decreases the rate of reaction.

True. It is of economic interest to have a higher rate of reaction as this implies a higher rate of production and hence a more efficient and sustainable process.

Increasing surface area increases the rate of reaction.

The time for a reaction to complete decreases when temperature is increased.

True. Decreasing particle size has the same effect as increasing surface area.

The amount of product formed remains the same when a catalyst is added, but it forms more quickly.

Collision theory explains how rates of reaction depend on the frequency and energy of collisions between reactant particles.

The minimum energy required for reactant particles to undergo a chemical reaction.

True. Increasing the concentration of a solution will increase the number of reactant particles in a given volume, allowing more frequent and successful collisions per second.

Increasing temperature:

Increasing the surface area of a solid reactant increases the rate of reaction because more particles are exposed to the other reactant, producing a higher number of collisions per second.

The number of collisions is proportional to the number of particles present.

A successful collision is a collision between reactant particles that leads to the formation of product molecules.

The symbol for activation energy is Ea.

False. Not all collisions result in a chemical reaction. Unsuccessful collisions happen when the colliding species do not have enough energy to break the necessary bonds.

A catalyst is a substance that increases the rate of a reaction without being used up itself.

A catalyst speeds up the rate of a reaction by providing an alternative pathway with lower activation energy.

False. Catalysts are not used up in the reaction.

False. Although catalysts are not part of the overall reaction, they may be written over the arrow in reaction equations, indicating the conditions.

True. Only small amounts of a catalyst are needed in a reaction as the catalyst is not used up.

You can show that a substance is a catalyst by:

The letter which represents the activation energy for a reaction using a catalyst is C.

True. Enzymes are nature's catalysts, biological substances that catalyse reactions in living cells.