3b Flashcards
(42 cards)
How ‘many’ is a mole?
6.023 x10 to the power of 23
What is the concentration of a solution measured in?
Moles per dm3 (i.e. moles per litre)
What is the formula for concentration?
Concentration = moles / volume
What are the two formulas you can use to work out number of moles?
Number of moles = concentration x volume
Number of moles = mass / RFM
How can you measure the amount of energy released by a chemical reaction and what can you do to prevent the amount of energy lost to surroundings?
Taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction. Reduce energy lost to surroundings by putting the polystyrene cup into a beaker of cotton wool to give more insulation and putting a lid on the cup to reduce energy lost by evaporation
What is an exothermic reaction?
One which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature
What is an endothermic reaction?
One which takes in energy from the surroundings, usually in the form of heat and usually shown by a fall in temperature
Is energy supplied or released in the breaking of existing bonds- is it endothermic or exothermic?
Energy must be supplied to break existing bonds- so bond breaking is an endothermic process
Is energy supplied or released when new bonds are formed- is it endothermic or exothermic?
Energy is released when new bonds are formed- so bond forming is an exothermic process
In an endothermic reaction, which is greater the energy required to break old bonds or the energy released when new bonds are formed?
The energy required to break old bonds is greater
In an exothermic reaction, which is greater the energy required to break old bonds or the energy released when new bonds are formed?
The energy released in bond formation
How is fuel energy calculated?
Calorimetry
What is the experiment for Calorimetry?
Water in copper can, record temp, weigh spirit burner & lid, spirit burner underneath can, heat water until 50ºc measure temp again weigh spirit burner again (with lid)
In exothermic reactions, is the energy change -ve or +ve?
Negative
In endothermic reactions, is the energy change -ve or +ve?
Positive
What happens to the activation energy in the presence of a catalyst?
The activation energy is lower
Is the reaction between hydrogen and water exothermic or endothermic?
Exothermic
What are the two ways you can use hydrogen as a fuel?
Burning it in an engine or by using it in a fuel cell
Hydrogen gas is burnt in oxygen as a fuel in the combustion engines of vehicles, name one pro and two cons of this
Only forms water so is very clean however you need a special and expensive engine and hydrogen is very hard to store
What is a fuel cell?
A fuel cell is an electrical cell thats supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity
Does a fuel cell run down or need recharging?
No, it’ll produce energy in the for, of electricity and heat as long as fuel is supplied
Why couldn’t fuel cells completely replace conventional petrol/diesel engines?
Hydrogen is a gas and so takes up more space to store, very explosive so difficult to store safely, hydrogen fuel made from hydrocarbons with needs fossil fuels or electrolysis
What kind of ions do metals always make?
Positive
What colour flame does Lithium give?
Crimson flame
