The Rate and Extent of Chemical Changes C6 Flashcards
What is the rate of a chemical reaction?
The rate of a chemical reaction is how fast the reactants are changed into products.
What is one of the slowest chemical reactions?
The rusting of iron is one of the slowest chemical reactions.
What are examples of slow reactions?
Other slow reactions include chemical weathering like acid rain damage to limestone.
What is an example of a moderate speed reaction?
An example of a moderate speed reaction would be magnesium reacting with an acid to produce bubbles.
What characterizes fast reactions?
Burning is a fast reaction, but explosions are even faster and release a lot of gas.
How can you find the speed of a reaction?
You can find the speed of a reaction by recording the amount of product formed or the amount of reactant used up over time.
What does a steeper line on a reaction graph indicate?
The steeper the line on the graph, the faster the rate of reaction.
What happens to the line on a reaction graph over time?
Over time, the line becomes less steep as the reactants are used up.
What does collision theory explain?
Collision theory explains how different factors affect the rate of reaction.
What is activation energy?
The minimum amount of energy that particles need to react is called the activation energy.
What factors increase the number of collisions in a reaction?
The collision frequency of reacting particles increases the number of collisions, making the reaction faster.
What is a successful collision?
A successful collision is one that results in the particles reacting to form products.
What are the four factors affecting the rate of reaction?
1) Temperature.
2) Concentration of a solution or pressure of gas.
3) Surface area.
4) Presence of a catalyst.
How does increasing temperature affect the rate of reaction?
Increasing temperature causes particles to move faster, leading to more frequent collisions and more energetic collisions.
How does increasing concentration or pressure affect the rate of reaction?
Higher concentration means more particles in the same volume, while higher pressure means the same number of particles in a smaller space, both increasing collision frequency.
How does increasing surface area affect the rate of reaction?
Breaking a solid into smaller pieces increases its surface area to volume ratio, allowing for more frequent collisions.
What is a catalyst?
A catalyst is a substance that speeds up a reaction without being used up in the reaction itself.
How do catalysts increase the rate of reaction?
Catalysts decrease the activation energy needed for the reaction by providing an alternative reaction pathway with a lower activation energy.
What are enzymes?
Enzymes are biological catalysts that catalyse reactions in living organisms.
What happens to the activation energy when a catalyst is used?
The activation energy is lowered when a catalyst is present.
Which reaction would have the fastest rate: powdered magnesium with water or hydrochloric acid with excess ethanoic acid?
Hydrochloric acid with excess ethanoic acid would have the fastest rate due to higher concentration.
What are the two ways to observe the rate of a reaction?
The rate of a reaction can be observed by how quickly the reactants are used up or how quickly the products are formed.
What are the units for measuring the rate of a reaction?
The units for rate may be in cm/s, g/s, or mol/s.
What is the first method of measuring the rate of a reaction?
1) Precipitation and Colour Change: You can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution.
How can you measure the time taken for a mark to disappear in a reaction?
You can observe a mark through the solution and measure how long it takes for the mark to disappear.
What is the second method of measuring the rate of a reaction?
2) Change in Colour: You can time how long it takes for the solution to lose (or gain) its colour.
What is a disadvantage of using visual methods to measure reaction rates?
The results are subjective; different people might not agree on the exact point when the mark disappears or the solution changes colour.
What is the third method of measuring the rate of a reaction?
3) Mass (Usually Gas Given Off): As the gas is released, the mass disappearing is measured on the balance.
How can the volume of gas produced be measured?
1) Using a gas syringe to measure the volume of gas given off during a reaction.
What does a quicker reading on the balance indicate?
The quicker the reading on the balance drops, the faster the reaction.
What is the most accurate method described for measuring reaction rates?
The mass balance method is the most accurate because it provides precise measurements.
What is a potential hazard when using a gas syringe?
If the reaction is too vigorous, you can easily blow the plunger out of the end of the syringe.
What is an example of a reaction that produces gas?
The reaction between solid NaCO and aqueous HCl releases CO2 (a gas).
What is turbidity in relation to a solution?
Turbidity refers to the cloudiness of a solution, which changes during a reaction.
What is the first step in the reaction with magnesium and dilute hydrochloric acid?
Start by adding a set volume of dilute hydrochloric acid to a conical flask and carefully place on a mass balance.
What should you do after adding magnesium ribbon to the acid?
Quickly plug the flask with cotton wool.
What should be recorded during the reaction?
Start the stopwatch and record the mass on the balance at regular intervals.
What is the effect of changing the concentration of hydrochloric acid on the reaction rate?
The results show the effect of decreasing the concentration of HCl on the rate of reaction.
What is the procedure for the reaction between sodium thiosulfate and hydrochloric acid?
Start by adding a set volume of dilute sodium thiosulfate to a conical flask, place it on a piece of paper with a black cross, add dilute HCl, and start the stopwatch.
What should be done to visualize the reaction between sodium thiosulfate and HCl?
Watch the black cross disappear through the cloudy sulfur and time how long it takes to go.
What should be kept constant in the experiments?
Variables such as the amount of magnesium ribbon and the volume of acid used should be kept the same each time.
What is the relationship between concentration and reaction time?
The higher the concentration, the quicker the reaction, and therefore the less time it takes for the mark to disappear.
What safety precaution should be taken during the experiment?
The experiment should be carried out in a well-ventilated place due to the release of sulfur dioxide.
What type of graph can be plotted from the results of the sodium thiosulfate and HCl reaction?
You could draw a graph of concentration against 1/time which will give you an approximate rate.
What does a rate of reaction graph show?
A rate of reaction graph shows the amount of product formed or amount of reactant used up on the y-axis and time on the x-axis.
How do you calculate the mean rate of reaction from a graph?
To find the mean rate for the whole reaction, work out the overall change in the y-value and divide this by the total time taken for the reaction.
How can you find the mean rate of reaction between two points in time?
You can find the mean rate of reaction between any two points in time by calculating the change in y over the change in x.
What is the formula for mean rate of reaction?
Mean rate of reaction = change in y / change in x.
How do you find the rate of reaction at a particular point in time?
To find the rate of reaction at a particular point in time, draw a tangent to the curve at that point and calculate the gradient of the tangent.
What is the process to draw a tangent to a curve?
1) Position a ruler at the point of interest. 2) Adjust the ruler until the space between the ruler and the curve is equal on both sides. 3) Draw a line along the ruler to create the tangent.
What is the rate of reaction at 3 minutes if the gradient is calculated?
The rate of reaction at 3 minutes was 0.27 g/min.
What should you do if the reaction finishes?
If asked to find the mean rate of reaction for the whole reaction, remember that the reaction finishes as soon as the line on the graph goes flat.
What happens in a reversible reaction?
The products can react to form the reactants again.
What occurs as reactants in a reversible reaction react?
Their concentrations fall, slowing down the forward reaction.
What happens as more products are made in a reversible reaction?
The concentrations of products rise, speeding up the backward reaction.
What is equilibrium in a reversible reaction?
It is when the forward and backward reactions occur at the same rate.
What is a closed system in the context of reversible reactions?
A closed system means that none of the reactants or products can escape and nothing else can get in.
Does equilibrium mean equal amounts of reactants and products?
No, equilibrium does not mean the amounts of reactants and products are equal.
What does it mean if equilibrium lies to the right?
The concentration of products is greater than that of the reactants.
What does it mean if equilibrium lies to the left?
The concentration of reactants is greater than that of the products.
What factors affect the position of equilibrium?
Temperature, pressure (for gases), and concentration of reactants and products.
What is the nature of reversible reactions regarding endothermic and exothermic processes?
If a reaction is endothermic in one direction, it will be exothermic in the other.
What happens when blue hydrated copper(II) sulfate is heated?
It drives the water off and leaves white anhydrous copper(II) sulfate powder.
What occurs when water is added to anhydrous copper sulfate?
It forms blue crystals of hydrated copper sulfate again.
What is dynamic equilibrium?
It involves lots of activity, but with no overall effect on concentrations.
What is Le Chatelier’s Principle?
Le Chatelier’s Principle states that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.
How can Le Chatelier’s Principle be used?
It can be used to predict the effect of any changes you make to a reaction system.
What happens to equilibrium when temperature is decreased?
If you decrease the temperature, the equilibrium will move in the exothermic direction to produce more heat.
What happens to equilibrium when temperature is increased?
If you raise the temperature, the equilibrium will move in the endothermic direction to try and decrease it.
How does pressure affect equilibrium involving gases?
Changing the pressure only affects an equilibrium involving gases.
What happens to equilibrium if pressure is increased?
If you increase the pressure, the equilibrium tries to reduce it by moving in the direction where there are fewer molecules of gas.
What happens to equilibrium if pressure is decreased?
If you decrease the pressure, the equilibrium tries to increase it by moving in the direction where there are more molecules of gas.
How does changing concentration affect equilibrium?
If you change the concentration of either the reactants or the products, the system will no longer be at equilibrium.
What happens if the concentration of reactants is increased?
If you increase the concentration of the reactants, the system tries to decrease it by making more products.
What happens if the concentration of products is decreased?
If you decrease the concentration of products, the system tries to increase it again by reducing the amount of reactants.
How does an increase in pressure affect the reaction N2 + 3H2 ⇌ 2NH3?
If you increase the pressure, the equilibrium shifts to the right, producing more NH3.
What is the significance of control in reversible reactions?
Control in reversible reactions is crucial for profitability in industry.
