Rates of Reaction and Energy Changes Flashcards
What is the equation for rate of reaction?
Amount of reaction used/product formed / time
What units could be used for rate of reaction?
g/s, cm^3/s and 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 and measure time and the 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 crossss 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
How 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
What 2 things could happen when the rate of reaction increases?
More frequent collisions and energy of collisions increases
How can the rate of a reaction be increased?
Increase temperature, concentration, surface area to volume ratio, pressure and add a catalyst
How does temperature affect the rate of reaction?
The reactants have more energy so more particles have more particles have energy above the activation energy meaning more collisions will be successful, collisions also occur more frequently because the particles have more kinetic energy
How does surface area affect the rate of reaction?
greater surface area means there are more exposed particles so more frequent successful collisions
How does catalyst affect the rate of reaction?
It provides an alternative reaction pathway with a lower activation energy so more particles will have sufficient energy to overcome the activation energy and react so more successful collisions occur in the same time
How does concentration affect the rate of reaction?
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?
There are more reacting particles in the same volume of gas so more frequent successful collisions occur
How can you find the rate of reaction using a graph?
X axis: time and Y axis: amount of reactant used/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
What is the shape of the curve if a graph is plotted to show time and the amount of gas given off during a reaction?
Initially the curve is very steep as the rate of reaction is relatively fast at the start, the curve becomes less steep add the reactants get used up because there are fewer successful collisions occurring and at the end, the graph is a flat line because all the reactant have been turned into products
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?
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 solution, mix both reactants in a polystyrene cup, record the highest temperature reached and calculate the temperature change
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 and lid on the reaction cup
What are exothermic and endothermic reactions in terms of bond breaking/forming?
Exothermic: energy released from breaking bonds is greater than the energy used to make bonds
Endothermic: energy released in forming new bonds is greater than the energy used to break old bonds
What types of reaction are exothermic?
Combustion and neutralisation
What is an example of an endothermic reaction?
Thermal decomposition and photosynthesis
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?
A graph showing showing the relative energies of reactant and products a well as the activation energy of a reaction
