C5- Energy changes Flashcards
- what happens to energy in chemical reactions
- Energy is conserved
- the amount of the energy in the universe at the start of the reaction is equal to the amount at the start of the reaction
What must happen for a reaction to transfer energy to surroundings
- the product molecules mss have less energy than the reactants
What does the conservation of energy mean
- the amount of energy in the universe never changes
What is an exothermic reaction
- one that transfers energy to the surroundings usually by heating - temperature around increases
What are examples of exothermic reactions and how do we use them everyday
- Exothermic reactions include combustion, oxidation and neutralisation
- Everyday uses include self heating cans and hand warmers
What is an endothermic reaction
- A reaction that takes energy from surroundings
- temperature of surroundings will decrease
What are the examples and everyday examples of exothermic reactions
- Thermal decomposition and reaction of citric acid and sodium hydrogen carbonate
- sport injury pack are based on exothermic reactions
How cam energy transfer be measured- practical
- take the temperature of the reagents - mix them in a polystyrene cup and measure to temperature at the end
- Loss of energy to surroundings
- can also measure the effect that variables have on energy transfer e.g concentration
- What are reaction profiles
- Diagrams that show the relative energies of reactants and products in a reaction and how energy changes over course of a reaction
What is activation energy
- Chemical reactions can only occur when reacting particles collide with each other with sufficient energy. the minimum energy that particles must have to react is called activation energy
What does a reaction profile look like in an exothermic reaction
- Products at l;over energy than reactants
- Difference in height represents energy change in reaction per mole
What does a reaction profile look like for an endothermic reaction
- Products are at a higher energy than the reactants
- Difference is height represents the overall energy change during the reaction in moles
What does the difference in height represent in reaction profiles
- The overall energy change during the reaction per mole
- How do bonds relate to energy during a reaction
- Energy must be supplied to brea bonds in the reactants
- Energy is related when bonds in products are formed
What happens in exothermic reactions regarding bond breaking