C3 Flashcards
Why might the mass of a reaction that occurs in an open vessel appear to decrease?
Because some of the products are in gaseous form and cannot be weighed/ contained.
List 2 ions with a -2 charge.
Any 2 of the following: Carbonate (CO3^-2), Sulfate (SO4^2-), Oxide (O^2-), Sulfide (S^2-)
Write the formula with the charge of a nitrate ion.
NO3^-
Balance the equation: Fe + Cl2 -> FeCl3
2Fe + 3Cl2 -> 2FeCl3
What do Ionic Equations do?
Only the useful bits of reactions are included.
What do half equations do?
Show the movement of electrons.
What is the mean mass of one atom of carbon?
24.3/ (6.022x 10 ^23) = 4.04 x 10^-23
Calculate the number of moles in 90g of water.
Mr of water = 18
n = m/ Mr
90/18 = 5 moles
Chlorine and potassium bromide react according to the equation: Cl2 + 2KBr —> Br2 + 2KCl
Calculate the mass of bromine produced when 23.8g of potassium bromide reacts in an excess of chlorine.
n = m/ Mr n = 23.8/ 39.1+ 79.9 n = 0.2 mol 2KBr : Br2 2:1 —> 0.1 mol n = m/ Mr 0.1 = m/ 79.9 x 2 m = 15.98 m ~ 16g
Do endothermic or exothermic reactions give out energy?
Exothermic.
84g of nitrogen gas are sealed in a vessel with 12g of hydrogen gas and heated. They react to produce ammonia. The equation for the reaction is: N2 + 3H2 —> 2NH3. What is the limiting reactant?
Mr (N2) = 2 x 14 = 28 Mr (H2) = 2 x 1 = 2 Ratio: N2 = 84/28 = 3 ,,,, H2 = 12/2 = 6 3:6 —> 1:2 The balanced equation gives a ratio of 1:3 , so H2 must be the limiting reactant.
What is activation energy?
The energy needed to start a reaction.
Is bonds forming endothermic or exothermic? Explain why.
Exothermic. The energy released by forming binds is greater than the energy used to break bonds.
How can bond energy be calculated?
Overall Energy Change = Energy required to break bonds - Energy released by forming bonds
Does a positive energy change mean an endothermic or exothermic reaction?
Endothermic.
