C7 Flashcards
What is the rule on energy transfer
It cannot be created or made it can only be transferred or conserved
What’s an exothermic reaction
When chemicals react energy is released into the surroundings. You can measure a rise in temperature and they have low power content
What’s an endothermic reaction
When chemicals react they need to absorb energy from the surroundings to be broken down. You can measure decrease in temperature of the surroundings
How are hand warmers a type of exothermic reaction
- it releases energy to the surroundings
- it can be re-used and are based on crystals from solutions of salt. A metal dish in the plastic starts the exothermic change
- small parts of the metal are scraped off and starts the crystallisation
- to re use it you boil it again to re-dissolve the crystals once cooled
What’s the chemical equation for hand warmers
Calcium oxide + water - calcium hydroxide
What’s an exothermic reaction that’s used to heat water
You press a button letting water and calcium oxide mix and exothermic reaction begins allowing coffee to boil
How do chemical cool packs work
It’s an endothermic reaction ideally containing ammonium nitrate and water and absorbs energy from the surroundings causing a reduction in temperature
They squeeze it and it releases ammonium nitrate which is put in water making a cold pack
What’s the reaction profile of an exothermic reaction
The reaction profile shows the products at a lower energy level to the reactants so when they react it’s released to the surroundings
What’s the reaction profile for an endothermic reaction
The products are at a higher energy level than the reactants. The energy transferred from the surroundings to the reaction causing temperature decrease
What is activation energy
The minimum energy needed before the collided particles of reactants cause a reaction. If lower than the activation energy they bounce off one another.
What must happen to beak bonds
Energy must be supplied so it’s an endothermic reaction
What happens when new bonds form
Energy is transferred to the surroundings
What is needed to break chemical bonds
Energy
How do you calculate bond energy
Energy to break chemical bonds in reactants
How much energy is released when new bonds are firmed in products
What is bond making
It’s an endothermic reaction as energy is needed and is supplied to break bonds and the new bonds transfer energy to the surroundings
