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neurologyYou need to know

• The rate of reaction is the change in the amount of a reactant used up or product formed per unit time.
• Rate of reaction can be calculated.
• The units for rate of reaction depend on the quantities measured, such as grams per second, cubic centimetres per second, or moles per second.
• The quantity of product formed usually increases quickly at first, then more slowly, and finally becomes constant when the reaction has finished.
• The quantity of reactant used up usually decreases quickly at first, then more slowly, and finally becomes constant when the reaction has finished.
• The gradient of a curve on a reaction graph shows the rate of reaction at that time; a steeper gradient means a faster rate.
• A tangent to a curve can be used to estimate the rate of reaction at a specific time by calculating the tangent's gradient.
• For a reaction to happen, reactant particles must collide with enough energy to overcome the activation energy.
• Increasing temperature increases the rate of reaction because particles have more kinetic energy, collide more often, and a greater proportion of collisions have enough energy to react.
• Increasing concentration of a solution or pressure of a gas increases the rate of reaction because there are more particles in a given volume, so collisions happen more often.
• Increasing the surface area of a solid reactant increases the rate of reaction because more particles are exposed for collisions.
• A catalyst increases the rate of reaction without being used up in the reaction, so it is not included as a reactant or product in the chemical equation.
• Catalysts increase the rate of reaction by providing an alternative reaction pathway with a lower activation energy.
• A reversible reaction is a reaction in which the products can react to reform the original reactants.
• A reversible reaction is represented in a chemical equation using the symbol ⇌.
• If a reversible reaction is exothermic in one direction, it is endothermic in the opposite direction, and the same amount of energy is transferred in reverse.
• Equilibrium is reached in a closed system when the forward and reverse reactions occur at the same rate, so the amounts of reactants and products remain constant.
• In a closed system at equilibrium, changing temperature, pressure, or concentration can change the relative amounts of reactants and products.
• If the concentration of a reactant is increased, the equilibrium shifts to make more products; if the concentration of a product is increased, the equilibrium shifts to make more reactants.
• For gaseous reactions at equilibrium, increasing pressure shifts the equilibrium towards the side with fewer moles of gas, while increasing temperature shifts the equilibrium in the endothermic direction.

• Collect rate of reaction data by measuring the change in mass, volume of gas produced, or change in colour or turbidity at regular time intervals.
• Calculate the mean rate of reaction from a table or graph by dividing the total quantity of reactant used or product formed by the total time taken.
• Plot a reaction rate graph with time on the x-axis and quantity of product formed or reactant used on the y-axis, using suitable scales and accurate points.
• Interpret reaction rate graphs by comparing gradients, identifying when the reaction is fastest, and recognising when the reaction has finished.
• Draw a tangent to a curve at a specified time, then calculate its gradient.
• Calculate a rate of reaction in mol/s when the amount of reactant used or product formed is given in moles.
• Explain the effect of temperature, concentration, pressure, surface area, and catalysts on rate using collision frequency and activation energy.
• Identify a catalyst in a reaction from evidence that it increases the rate and is chemically unchanged at the end of the reaction.
• Write reversible reaction equations using `⇌` and describe the forward and reverse reactions.
• Predict qualitatively how changes in temperature, pressure, or concentration affect the position of equilibrium using the information given about the reaction.