Rate Of Reactions Flashcards
What is the ‘rate’ of a chemical reaction?
-A measure of how quickly the reactants are converted into products
What are the formulas for rate of reaction
-rate of reaction= amount of reactant used/time
-rate of reaction=amount of product formed/time
what can the quantity of reactant be measured in?
mass in grams
What can quantity of product be measured in?
volume in cm^3
What are the units of rate of reaction?
g/s or cm^3/s
How do scientists determine the exact rate of reaction?
-using tangents
What is the collision theory?
-chemical reactions can only take place when reacting particles collide with each other. The collisions must have sufficient energy
What is the rate of a chemical reaction determined by?
-the frequency of successful collisions
What does frequency mean
-the number of successful collisions per second
Describe the relationship between rate and concentration
-if the concentration increases so does the rate
-the rate is proportional to the concentration
What are the five factors which affect the rate of chemical reactions?
-concentration
-pressure
-surface area
-temperature
-catalysts
What is the activation energy?
What happens if we increase the concentration of reactants in solutions?
-increases the frequency of collisions and so increases the rate of reaction
What happens if we increase the pressure of reacting gases
-increases the frequency of collisions and so increases the rate of reaction
What happens if we increase the surface area of solid reactants?
-increases the frequency of collisions and so increases the rate of reaction
What happens if we increase the temperature?
-increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.
What is a catalyst?
-substances that speed up chemical reactions without being changed or used up during the reaction
What do enzymes act as?
-enzymes act as catalysts in biological systems
How does sulfur affect the solution?
-sulfur makes the solution go cloudy.
-scientists call this cloudiness turbidity
-we can use this to see how long the reaction takes to finish
What is the method for the disappearing cross experiment practical
-use a measuring cylinder to put 10cm^3 of sodium thiosulfate solution into a conical flask
-place the conical flask onto a printed black cross
-add 10cm^3 of hydrochloric acid into the conical flask
-swirl the solution and start a stopwatch
-solution will turn cloudy and we stop clock when we can no longer see cross
-carry out experiment again using lower concentrations of sodium thiosulfate solution
-repeat the whole experiment and calculate mean values for each concentration of sodium thiosulfate solution.
When is a measurement reproducible?
-if it can be repeated by another person
-or using a different technique or equipment and still getting the same result.
what is the problem with the disappearing cross experiment?
-different people have different eyesights.
What is the method to measure the volume of the gas produced by a reaction?
-use a measuring cylinder to place 50cm^3 of hydrochloric acid into a conical flask
-attach the conical flask to a bung and delivery tube
-now place the delivery tube into a container filled with water
-place upturned measuring cylinder also filled with water over the delivery tube.
-add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch.
-the reaction produces hydrogen gas which trapped in measuring cylinder
-every ten seconds, measure the volume of hydrogen gas in measuring cylinder
-continue until no more hydrogen is given off.
-repeat experiment using different concentrations of hydrochloric acid
How do catalysts affect the activation energy?
-catalysts decrease the activation energy: this increases the proportion of particles with energy to react
-catalysts provide a different pathway for a chemical reaction that has a lower activation energy.
Describe and explain the effect of increasing temperature on the rate of reaction
-as temperature increases, kinetic energy of particles increase leading to more energetic collisions
-also, they move faster, so they collide more frequently
-rate and temperature are not directly proportional to each other.
Describe and explain the effect of increasing concentration on the rate of reaction
-concentration increase leads to faster reaction
-more reactants lead to more frequent collisions
Describe and explain the effect of increasing pressure of a gas on the rate of reaction
-it increases the number of gas molecules in the same volume and so increases frequency of collisions and therefore increases the rate of reaction
-volume and pressure are inversely proportional to each other
Describe and explain the effect of increasing surface area
-if solid reactants are in smaller pieces, they have a greater surface area.
-increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction
-block of magnesium reacts slower with acid then magnesium powder
What is a reversible reaction?
-when the products of a reactant can react backwards to produce the original reactants
When is dynamic equilibrium reached?
-in a closed system, when the forward and reverse reactions occur at the same rate and the concentrations of reactants and products remain constant
Describe Le Chatelier’s principle
-if a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract change and restore the equilibrium
Describe the effect of changing temperature on the position of the equilibrium
-if the temperature of a system at equilibrium is increased :
•the relative amount of products at equilibrium increases for an endothermic reaction
-the relative amount of products at equilibrium decreases for an exothermic reaction
Describe the effect of changing the concentration of reactant and product on the position of the equilibrium
-if the concentration of one of the reactants or products are changed , the system is no longer at equilibrium and the concentrations of all the substances will change until equilibrium is reached again.
-if the concentration of a reactant is increased, more products will be formed until equilibrium is reached again.
-if the concentration of a product is decreased,more reactants will react until equilibrium is reached again
Describe the effect of changing pressure on the position of equilibrium
-an increase in pressure causes the equilibrium position to shift toward the side with the smaller number of molecules as shown by the symbol equation for that reaction.
-A decrease in pressure causes the equilibrium position to shift toward the side with the larger number of molecules as shown by the symbol equation for that reaction
-pressure has no effect on the reactions where the numbers of gas molecules are equal on both sides of the equation
Describe the effect of a catalyst on the position of the equilibrium
-no effect
-it just speeds up both forward and backward reactions equally
