Topic 7 - rates of reaction and energy changes Flashcards
What is the equation for rate of reaction?
Amount of reactant used or product formed/ time
What units could be used for rate of reaction?
G/s
Cm^3/s
Mol/s
How can you measure the rate of reaction when a gas is given off?
Measure time and collect gas in an upside down measuring cylinder in a trough of water or in a gas syringe to measure the volume of gas produced
Measure time and change in mass
How can you measure the rate of reaction when a precipitate is formed?
Put a black cross below a beaker containing one reactant. Time how long it takes for the cross to disappear after the second reactant is added
Why is using the precipitation method to investigate rate of a reaction not very accurate?
It’s subjective so people are likely to disagree over the exact point at which the cross is no longer visible
How can you measure rate of reaction using a digital balance?
When a gas is produced as this will cause mass to decrease. The experiment can be carried out on a digital balance and the rate of reaction can be calculated by recording the mass at regular time intervals
What does ‘activation energy’ mean?
The minimum amount of energy required for a reaction to occur between two reacting particles
What must happen for a reaction to occur?
Particles must collide at the correct orientation with sufficient energy to react
In terms of particles, what 2 things could happen when the rate of reaction increases?
More frequent collisions
Energy of collisions increases
How can the rate of a reaction be increased?
Increase the temperature Increase the concentration Increase the surface area to volume ratio Add a catalyst Increase the pressure (for gases)
How does temperature affect the rate of reaction?
It increases it because the reactants have more energy so more particles have activation energy meaning more successful collisions
How does surface area affect the rate of reaction?
It increases because a greater surface area means there are more exposed particles so more frequent successful collisions
How does a catalyst affect the rate of reaction?
Increases because it provides an alternate reaction pathway with lower activation energy. More particles will have sufficient energy and react so more successful collisions occur in the same time.
How does concentration affect the rate of reaction?
Increasing concentration increases the rate of reaction. This is because there are more reacting particles in the same volume so there are more frequent successful collisions.
How does pressure affect the rate of a gaseous reaction?
Increases e are more reacting particles in the same volume of gas so more frequent successful collisions occur
Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide. How could you measure the rate of reaction?
Since gaseous carbon dioxide is released, the rate can be measured by using a digital balance to measure the change in mass over a period of time.
Marble chips react with hydrochloric acid to produce calcium chloride, water and carbon dioxide, how could the rate of this reaction be increased?
Increase the surface area of the marble chips by turning them into a powder
Increase concentration of acid
Increase temperature
After completing an experiment, how can you find the rate of reaction using a graph?
X axis: time
Y:axis amount of reactant used or product formed
Draw a tangent to a point on the graph and find the gradient of this line to find the rate of reaction at that time
A graph showing time and the amount of gas given off during an experiment has a steep gradient. What does this tell you about the rate of the reaction?
Fast rate of reaction
What is a catalyst?
A substance which speeds up the rate of a reaction without being chemically changed at the end
How does a catalyst speed up the rate of a reaction?
It provides an alternate reaction pathway with a lower activation energy
What are enzymes?
Enzymes act as biological catalysts that increase the rate of reactions in living cells
Which enzyme is used to produce ethanol from glucose?
Yeast
What does exothermic mean?
A reaction that gives out energy to the surroundings
What does endothermic mean?
A reaction that takes in heat energy from the surroundings
Are neutralisation reactions endothermic or exothermic?
Exothermic
Are displacement reactions endothermic or exothermic?
Either exothermic or endothermic
Is a salt dissolving in water endothermic or exothermic?
Either exothermic or endothermic
Are precipitation reactions endothermic or exothermic?
Exothermic
How could you measure the temperature change of a neutralisation reaction?
Measure initial temperature of the solutions
Mix both reactants in a polystyrene cup
Record the highest temperature reached
Calculate the temperature change
When measure it the temperature change of a reaction, heat loss means that measurements may be inaccurate. How could heat loss be minimised during an experiment?
Use polystyrene cup
Place reaction cup in a beaker full with cotton wool for extra insulation
Lid on the reaction cup
In terms of bond energies, what happens during a chemical reaction? Describe exothermic and endothermic reaction in terms of bonds breaking/forming
Energy is needed to break bonds and is released when bonds are made
Exothermic: energy released from breaking bonds is greater than the energy used to make bonds
Endothermic: energy released in forming new bond is greater than the energy used to break only bonds
What two types of reaction are exothermic?
Combustion
Neutralisation
How can the energy change of a reaction be calculated from bond energies?
Total energy of bonds broken - total energy of bonds made
If the energy change of a reaction is negative, is the reaction exothermic or endothermic?
Exothermic, energy has been lost to the surroundings
What is a reaction profile p?
A graph showing the relative energies of reactants and products, as well as the activation energy of a reaction
