C7- Rates of reaction and energy changes Flashcards
(26 cards)
What is the equation for average rate of reaction?
Average rate of reaction= amount of reactant used or amount of product formed/ Time
Give three ways that you can measure rate of reaction
Measuring change in mass
Precipitation reaction
Volume of gas given off
What is activation energy?
The minimum energy that particles need to react when they collide
What happens to the rate if you increase the concentration/pressure?
- More particles of reaction reactant in the same volume. This makes collisions more likely, so the reaction rate increases
In a gas, increasing the pressure means that the particles are more crowded. This means that the frequency of collisions between particles will increase
What is a catalyst?
A substance which increases the rate of reaction without being chemically changed or used up in the reaction
What is an endothermic reaction?
A reaction which takes in energy from surroundings, shown by a decrease in temperature of the surroundings
How does a precipitation reaction work for measuring rate of reaction?
1) This method works for any reaction where mixing two see-through solutions produced a precipitate which clouds the solution
2) You mix the two reactant solutions and put the flask on a piece of paper that has a mark on it
3) Observe the mark through the mixture and measure how long it takes for the mark to be obscured. The faster it disappears, the faster the reaction
4) The result is subjective
How can you measure change of mass for a rate of reaction experiment?
You can measure the rate of a reaction that produces a gas using a mass balance
As the gas is released, the lost mass is easily measured on the balance. The quicker the reading on the balance drops, the faster the reaction
How can you measure volume of gas given off for a rate of reaction experiment?
Involves the use of gas syringe to measure the volume of gas given off.
The more gas given off during a set time interval, the faster the reaction
You can tell the reaction has finished when no more gas is produced
What happens to rate of reaction when you increase the surface area?
The particles around it will have more area to work on, the the frequency of collisions will increase
This means that the rate of reaction is faster for solids with a larger surface area to volume ratio
What is the experiment to investigate how surface area affects rate?
Set up a conical flask with a bung and a gas syringe going into the conical flask
Measure the volume of gas producing using the gas syringe. Take readings at regular time intervals and record the results in a table
Repeat the experiment with exactly the same volume of concentration of acid, and exactly the same mass of marble chips, but with the marble more crunched up
Then repeat with the same mass of powdered chalk.
What is the experiment to investigate how concentration affects rate?
Set up a conical flask with a bung and a gas syringe going into the conical flask
Measure the volume of gas producing using the gas syringe. Take readings at regular time intervals and record the results in a table
Repeat the experiment with exactly the same mass and surface area of the marble chips but using different concentrations of acid.
What is the experiment to investigate how temperature effects rate of reaction?
Measure out fixed volumes of sodium thiosulfate and hydrochloric acid using a measuring cylinder
Use a water bath to gently heat both solutions to the desired temperature before you mix them
Mix the solutions in a conical flask. Place the flask over a black mark on a piece of paper which can be seen through the solution. Watch the black mark disappear through the cloudy yellow sulfur and time how long it takes to go
The depth and volumes of liquid must be kept the same each time
What two things does the rate of a chemical reaction depend on?
The collision frequency of reacting particles.
The energy transferred during a collision. The minimum energy that particles need to react when they collide is called the activation energy. Particles need to collide with at least the activation energy for the collision to be successful
How does increasing the temperature affect rate of reaction?
When the temperature is increased, the particles move faster. If they move faster, they’re going to have more collisions
Higher temperatures also increase the energy of the collisions, since the particles are moving faster.
How do catalysts work?
Catalysts work by decreasing the activation energy, they do this by providing an alternative reaction pathway that has a lower activation energy
What is an exothermic reation?
One that gives out energy to the surrounding, shown by a rise in temperature
Draw the reaction profile for an endothermic reaction. labelling activation energy
Draw the reaction profile for an exothermic reaction, labelling activation energy
What is the experiment to follow the temperature change of a reaction?
Put a polystyrene cup into a larger beaker of cotton wool (the cotton wool gives insulation to help limit energy transfer to or from the reaction mixture)
Add a known volume of your first reagent to the cup
Measure the initial temperature of the solution
Add a measured mass/volume of your second reagent and stir the reaction mixture
Put a lid on the cup to reduce any energy loss by evaporation
Record the minimum/maximum temperature and calculate the temperature change
How can you measure the temperature change when dissolving salts in water?
By adding salt to a polystyrene cup of water and measuring the change in temperature when the salt has dissolved
Are neutralisation reactions exothermic or endothermic?
exothermic, except for the reaction between ethanoic acid and sodium carbonate
Are displacement reactions endo, or exothermic
Exothermic
Are precipitation reactions endo or exothermic?
Exothermic
