12 pens for writing chemical formulas cost
12*2=24 dollars
12 pads cost
12*3=36 dollars
1)
12*2=24
12*3=36
2)
12*2+12*3=60 dollars
3) 12*(3+5)=60 dollars
Answer:
Enthalpy change = 74.36 kJ
Explanation:
Enthalpy change is defines as the heat absorbed or evolved during a chemical reaction at constant pressure and volume
Reaction:
H2O(l) --> H2O(g)
DHr = mCsDT
Where m is the mass of water
Cs is the specific heat capacity
DT is the temperature difference
= 31.6 * 4.18 * (25 - 3.2)
= 2879.518 J
DHvap = 44kJ/mol
Moles of water = mass/molecular weight
Molecular weight = (1*2) + 16
= 18g/mol
Moles of water = 31.6/18
= 1.756 moles
DHvap = 44 * 1.756
= 77.244kJ
DH = DHproduct - DHreactant
DHproduct = DHvap = 77.24kJ
DHreactant = DHr = 2879.518J = 2.880kJ
= 77.24 - 2.880
DH = 74.36kJ
Enthalpy change = 74.36 kJ
Answer:
Explanation:
mass of 1mole of brick = mass of 1 brick x avagadro number
= 4 kg x 6.022 x 10^23 bricks = 2.4 x 10^24 kg
No. of moles of bricks have a mass equal to the mass of the earth
= mass of earth / mass of 1 mole of brick
= [ 6 x 10^27 ] / [ 2.4 x 10^24 ]
= 2.5 x 10^3
= 2500 moles
It will double
Key
P = pressure of the gas
n= number of moles of the gas
V= volume of the gas
R = the gas constant
T= absolute temperature of the gas
If V is halved when n and T remain the same
Answer:
See below
Step-by-step explanation:
- Hydrogen either reacts with or is formed by reactions with many other elements, so chemists could use it directly to determine their relative masses.
- Hydrogen has the smallest atomic mass, so it was convenient to give H a relative atomic mass of 1 and assign those of other elements as multiples of this number.
The O = 16 scale became the standard in 1903 and carbon-12 was chosen in 1961.
