Energy Flashcards
(27 cards)
What is meant by average bond enthalpy?
When one mole of bonds is broken (gaseous covalent)
What is meant by activation enthalpy?
The minimum energy required for a reaction to take place (for the reactants to react)
What is meant by standard enthalpy change of combustion?
When one mole of a substance completely combusts
What is meant by standard enthalpy change of formation?
When one mole of a compound is formed from its elements
What is meant by standard enthalpy change of neutralisation?
When one mole of water is formed from a neutralisation reaction
State the conditions of temperature and pressure used for standard enthalpy measurements
298K and 100kPa
Why do Br2 and I2 not exist in the gaseous state under standard conditions?
Because energy is needed to break London forces between molecules
How can you calculate the standard enthalpy change of combustion?
Products - reactants
How can you calculate the standard enthalpy change of formation?
Products - reactants
How can you calculate the standard enthalpy change?
Reactants - products
State why the enthalpy change of formation cannot be determined
- Activation energy too high
- Rate is too slow
- Do not react together
How can you calculate energy change?
q = mcΔT
The calculated value of enthalpy of combustion, from a experiment, is different from the value obtained from data books. What are the reasons for this difference?
- Heat released to the surroundings
- Incomplete combustion
- Non-standard conditions
C4H10(g) + 6.5O2(g) -> 4CO2(g) + 5H2O(l)
Explain why this equation represents the standard enthalpy change of combustion of butane
One mole of butane completely combusts in oxygen
What is meant by an exothermic reaction?
- More energy is released by forming bonds than energy required when breaking bonds
- Gives out energy
- ΔH is negative
What is meant by an endothermic reaction
- More energy is required for bond breaking than is released by bond making
- Takes in energy
- ΔH is positive
Explain why increasing the concentration increases the rate of a reaction
- More particles per unit volume
- More frequent collisions with the correct orientation
Describe and explain the effect of increasing the pressure on the rate of a reaction
- Increased rate
- More molecules per unit volume
- More frequent collisions with the correct orientation
Describe and explain the effect of decreasing the pressure on the rate of a reaction
- Decreased rate
- Less molecules per unit volume
- Less frequent collisions with the correct orientation
Describe and explain the effect of increasing the temperature on the rate of a reaction
- Increased kinetic energy (more particles have higher energy than the activation enthalpy)
- More frequent collisions with the correct orientation as they move faster and further
- Increased rate
Describe and explain the effect of increasing the surface area on the rate of a reaction
- Increased number of exposed reactant particles
- More frequent collisions with the correct orientation
Outline how a catalyst increases the rate of a chemical reaction
- Allows the reaction to proceed via a route with lower activation energy
- So that a greater proportion of molecules exceed the activation energy
Explain why use of a catalyst reduces energy demand and benefits the environment
- Reduces CO2 emissions
- Less fossil fuels
- Lower temperatures
State the ways that the use of catalysts helps chemical companies to make their processes more sustainable and less harmful to the environment
- Greater atom economy
- Lower energy demand
