Unit 1 - Topic 1 - Rates of Reaction Flashcards
What are the different ways we can know a chemical change has occurred?
- If gas is produced
- If the colour changes
- If there is a smell
- If there is a change in temperature - Endothermic/Exothermic Reaction
- If a precipitate is produced
Give 3 examples of physical changes.
- Melting/Freezing
- Boiling/Condensing
- Dissolving/Evaporating
What is the difference between a chemical reaction and a physical change?
A physical change usually involves a change in state and can easily be reversed. Chemical reactions are more difficult to reverse.
What is the speed of the reaction called?
Reaction Rate
Give an example of a very slow reaction.
Rusting
Extremely fast reactions can be…
Explosive
What is a exothermic reaction?
A type of reaction that releases energy to the surroundings. The temperature increases.
What is an endothermic reaction?
A type of reaction which takes energy from the surroundings. The temperature decreases.
What is a precipitation reaction?
A type of reaction that produces an insoluble salt by mixing 2 solutions. The insoluble salt is called precipitate.
How many methods are there to collect gases?
4
What are the 4 methods of collecting gases?
- If the gas is insoluble in water and less dense than air, we use downward displacement of water.
- If the gas is soluble in water and less dense than air, we use upward delivery.
- If the gas is soluble or insoluble in water and more dense than air, we use downward delivery.
- The most reliable method of measuring the volume of gas collected is using a gas syringe.
Describe how the downward displacement of water is used to collect gases.
The gas bubbles through the water and is collected at the top of the measuring cylinder.
The insoluble gas replaces the water meaning the volume of gas produced can be measured.
What gases are collected by the downwards displacement of water method?
Oxygen and Hydrogen.
Why is the downwards displacement of water method not the most accurate way of collecting gases?
Because some of the gas will dissolve in the water.
Describe how upward delivery is used to collect gases.
The gas cannot be collected in water as it will dissolve.
The gas is less dense than air so it will rise.
Describe how downward delivery is used to collect gases.
The gas will sink because it is denser than air. Water is not required.
Describe how a gas syringe is used to collect gases.
This method is more reliable because no or less gas is lost through error e.g. not letting the delivery tube in the water and measuring the cylinder fast enough, resulting in gas being lost.
What is the link between a line on a graph and the rate of reaction?
The steeper the line, the faster the rate of reaction.
In all reactions, the rate decreases as the reaction proceeds. Why?
The reactants are being used up or running out.
When does a reaction occur?
A reaction occurs when the hydrochloric acid particles collide with the marble particles.
Explain collision theory.
For particles to react, they must collide with each other to form products.
To speed up a reaction there must be more collisions.
What happens when a solid reacts?
When a solid reacts, it is only the particles on the surface area of the solid which come in contact with the other reactant.
Do large lumps have a large or small surface area?
Small
Using collision theory, explain why the reaction rate is decreased with large lumps.
Less particles are exposed to the surface, so less particles collide. This means the rate of reaction is slower.
Do small lumps have a large or small surface area?
Large
Using collision theory, explain why the reaction rate is increased with small lumps.
More particles are exposed to the surface, so more particles collide. This means the rate of reaction is faster.
What is concentration?
The concentration of a solution is a measure of the number of particles of chemical in every drop of solution.
Does having a lower concentration of a reactant increase or decrease the reaction rate?
Decrease
Using collision theory, explain why the reaction rate is decreased in a lower concentration.
If the concentration is lower, less particles are in the reaction mixture, therefore there will be less successful collisions. This results in a slower reaction.
Does having a higher concentration of a reactant increase or decrease the reaction rate?
Increase
Using collision theory, explain why the reaction rate is increased in a higher concentration.
If the concentration increases, there are more particles in the reaction mixture, therefore there will be more successful collisions. This results in a faster reaction.
What happens when a substance is heated?
When a substance is heated up its particles move about faster as they have more energy.
Do the particles move slower or faster in a lower temperature?
Slower
Do the particles have more or less energy in a lower temperature?
Less
Using collision theory, explain why the reaction rate is decreased in a lower temperature.
A lower temperatures, particles move slower. This means there are less collisions, so there is a slower reaction rate.
Do the particles move slower or faster at higher temperatures?
Faster
Do the particles have more or less energy at higher temperatures?
More
Using collision theory, explain why the reaction rate is increased at a higher temperature.
A higher temperatures, particles move faster. This means there are more collisions, so there is a faster reaction rate.
What is a catalyst?
A catalyst is a chemical which speeds up the rate of reaction without being changed. The catalysts are not used up so can be used to speed up multiple reactions.
Why would catalysts be useful in industry?
Reduces cost due to the catalyst allowing reactions to be faster at lower temperatures. Also catalysts can be reused multiple times
What are enzymes?
Enzymes are biological catalysts. They speed up chemical reactions in the body. For example, catalase is the enzyme present in all living cells. Like manganese dioxide, it speeds up the breakdown of hydrogen peroxide to water and oxygen.
What is the reaction rate?
The rate of a reaction is a measure of how quickly a reactant is used up by a reaction, OR how quickly a product is made by a reaction.
What is the formula for finding the average reaction rate?
Time interval for the change
What graphs can be used to calculate the average reaction rate?
A graph plotted from the data obtained by measuring the mass, concentration or gas volume, as they vary with time during a reaction, can be used to calculate the average rate.
What are the units for concentration change per minute?
mol /-1 min-1
What are the units for gas volume change per second?
cm3 s-1
What are the units for mass change per hour?
g hr-1
What is the test for Oxygen?
It relights a glowing splint.
What is the test for Hydrogen?
Burns with a pop.
What are the 2 tests for Carbon Dioxide?
Puts out a flame
Turns limewater from colourless to cloudy.
Which of the 2 tests for Carbon Dioxide is official and why?
The official test for Carbon Dioxide is that it turns limewater from colourless to cloudy. This is because Nitrogen can also put out a flame.
