Unit 2 section 1&2 chemistry 0.0 / 5 ? ChemistrylolASAQA Created by: Callumjamessmith1998Created on: 25-02-15 20:44 What is enthalpy change? The heat energy transferred in a reaction of constant pressure 1 of 23 What is the enthalpy change of an exothermic reaction and why? Negative enthalpy change or negative change in energy because energy is given out in an exothermic reaction 2 of 23 Are bonds broken or created in an exothermic reaction? Bonds are broken, so energy is given out which means negative enthalpy change 3 of 23 what is the equation for enthalpy change? total energy absorbed - total energy released (found by using bond energy) 4 of 23 What are the 3 types of enthalpy change? Reaction, formation and combustion 5 of 23 What two things do you need to know to measure enthalpy change in a lab? Number of moles of reactant and change in temp 6 of 23 What is Hess's Law? The total enthalpy change of a reaction is the same no matter which path you take 7 of 23 what is the activation energy? The minimum amount of energy needed for the particles to start reacting 8 of 23 What is the maxwell- Boltzmann distribution? Graph of no of molecules (Y) and kinetic energy (x) with a curve shape 9 of 23 What happens when you increase the temperature? The peak is lower and more atoms are in the activation energy zone 10 of 23 What happens when you increase the concentration? peak is higher on top of the activation energy and the top 11 of 23 What does a catalyst do to the graph? Moves the activation energy to the left because its lowered 12 of 23 why dont all collisions end up in a reaction? have to be correctly orientated and have enough kinetic energy 13 of 23 What is the dynamic equilibrium? When the forward and backward reaction occur at the same rate in a closed system? 14 of 23 What 3 things alter equilibrium? Concentration, temperature, pressure 15 of 23 What happens if the equilibrium is pushed left? More reactants 16 of 23 What does a catalyst do to the position of the equilibrium? Nothing 17 of 23 What happens if you increase the concentration of reactants? equilibrium is pushed towards the products giving more products 18 of 23 What happens to the equilibrium when you increase the pressure shifts to the side with fewer gas molecules 19 of 23 what happens when you increase the temperature? Favours endothermic side as it absorbs the added head 20 of 23 What two things are added together to make ethanol and what conditions? ethene + h20(steam), 60-70ATM, 300 degress c and phosphoric acid catalyst 21 of 23 Why do companies pick a high temp on this reaction? Low temp favours the reaction, but slows down the reaction rate so its better to increase it 22 of 23 Why do companies pick a lower pressure? high pressure favours the ethanol side, but more expensive because better equipment is needed 23 of 23
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