Energetics Flashcards
Define an exothermic reaction
a reaction that gives out energy to the surroundings
Define an endothermic reaction
a reaction takes in energy from the surroundings
Define in system
within reaction
Define surroundings
outside reaction
What represents the activation energy for energy profile diagram
the arrow from the reactants energy level to the peak
What does exothermic reactions reactants and products in an energy profile diagram
The energy level of the products is less than the energy level of the reactants. energy has been transferred to surroundings
What are the endothermic reactions reactants and products in an energy profile diagram
Energy level of the products is more than then the energy level of the reactants as energy has been transferred from the surroundings to the product
An application of exothermic reactions
hand warmers
application of endothermic reactions
sports injury packs
examples of exothermic reactions
oxidation reactions, combustion reactions and neutralisation reactions
examples of endothermic reactions
thermal decomposition of metal carbonates, reactions of acids with metal hydrogencarbonates
What is the equation for energy change
energy change = mass of solution (g) * heat capacity (c) * temp. change
What are the steps to work out change in heat energy
1) Use this equation to calculate energy change
2) Work out moles of reactants used
3) Divide q by the number of moles of the reactant not in excess to give change in heat. (-q)/n=change in heat (j,mol-1 )
4) Add a sign and unit, divide by a thousand to convert jmol -1 to Kjmol -1
What is the relationship between adding sodium hydroxide and temp.
Graph shows as sodium hydroxide added, temp. increases. This is as more sodium hydroxide added more reacts and more heat is released as it is an exothermic reaction
Why does the temp. level off after a certain temp.
• At a certain volume maximum temp. levels off as sodium hydroxide is in excess now and not able to react
Why may the temp. decrease after a certain point
May decrease after this point as we are adding more and more solution so energy will be spread out so max temp. decreases
Describe how you would investigate temp. change using the neutralisation reaction of HCL and sodium hydroxide
1) Measuring cylinder to measure 30cm of dilute HCL
2) Transfer acid into polystyrene cup and put it into a beaker
3) Thermometer to measure temp. Of acid
4) Use measuring cylinder to measure 5cm2 of sodium hydroxide and add it to the solution
5) Thermometer and lid added with bulb of thermometer must be in lid and read highest temp.
6) Rinse out and dry polystyrene cup and repeat experiment but increasing 5cm2 of sodium hydroxide each time until 40cm2
7) Then do it again to calculate a mean
What happens to bonds during a chemical reaction
- Energy must be supplied to break bonds in the reactants
- Energy is released when bonds in the products are made
how do you work out the energy change of a reaction
• Energy Change of a reaction = Bonds broken – Bonds formed
Why do exothermic reactions have a negative energy change
more energy is released in making new bonds than is needed to break bonds as energy is released to surroundings. Thus as -ve overall energy change
Why do endothermic reactions have a positive energy change
• Endothermic reactions; more energy is needed to break bonds than is released making new bonds. Thus +ve overall change
