If the heating is done on one small area on the top, there will be convection. If the heating is restricted to a small fraction of the heating area, then within that area the heating will go deeper than anywhere else on the surface. Then unheated area will have a shallower region of high temperature. Then some convection will occur in the deeper layers, causing some motion on top.
This happens quite a bit during welding. Convection is very significant in welding, even when the heating is from the top.
Explanation:
The balanced equation of the reaction is given as;
Mg(OH)2 (s) + 2 HBr (aq) → MgBr2 (aq) + 2 H2O (l)
1. How many grams of MgBr2 will be produced from 18.3 grams of HBr?
From the reaction;
2 mol of HBr produces 1 mol of MgBr2
Converting to masses using;
Mass = Number of moles * Molar mass
Molar mass of HBr = 80.91 g/mol
Molar mass of MgBr2 = 184.113 g/mol
This means;
(2 * 80.91 = 161.82g) of HBr produces (1 * 184.113 = 184.113g) MgBr2
18.3g would produce x
161.82 = 184.113
18.3 = x
x = (184.113 * 18.3 ) / 161.82 = 20.8 g
2. How many moles of H2O will be produced from 18.3 grams of HBr?
Converting the mass to mol;
Number of moles = Mass / Molar mass = 18.3 / 80.91 = 0.226 mol
From the reaction;
2 mol of HBr produces 2 mol of H2O
0.226 mol would produce x
2 =2
0.226 = x
x = 0.226 * 2 / 2 = 0.226 mol
3. How many grams of Mg(OH)2 are needed to completely react with 18.3 grams of HBr?
From the reaction;
2 mol of HBr reacts with 1 mol of Mg(OH)2
18.3g of HBr = 0.226 mol
2 = 1
0.226 = x
x = 0.226 * 1 /2
x = 0.113 mol
The mass of sulfur in a sample of CaSO4 with a mass of 65.8 g is 15.50g.
<h3>How to calculate mass of an element in a compound?</h3>
According to this question, a 10.4 g sample of CaSO4 is found to contain 3.06 g of Ca and 4.89 g of O.
This means that the mass of sulfur in the 10.4g of CaSO4 is 10.4g - (3.06g + 4.89g) = 10.4g - 7.95g = 2.45g
Next, we calculate the percent ratio of each element in the compound; CaSO4.
- Ca = 3.06g/10.4g × 100 = 29.42%
- S = 2.45g/10.4g × 100 = 23.56%
- O = 4.89g/10.4g × 100 = 47.02%
According to this question, a sample of CaSO4 with a mass of 65.8 g is given. The mass of each element in this compound is as follows:
- Ca = 29.42/100 × 65.8g = 19.36g
- S = 23.56/100 × 65.8g = 15.50g
- O = 47.02/100 × 65.8g = 30.94g
Therefore, the mass of sulfur in a sample of CaSO4 with a mass of 65.8 g is 15.50g.
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Answer:
1. Increasing the concentration of the acid
2. Increasing the temperature
Explanation:
CaCO₃ + 2HCl ⟶ CaCl₂ + H₂O + CO₂
Increasing the concentration of the acid increases the number of hydronium ions in contact with the surface of the CaCO₃ per unit time.
Increasing the temperature increases the kinetic energy of the hydronium ions, so they hit the surface of the CaCO₃ mor frequently and with greater force.
3. is wrong. The bigger the pieces, the smaller the surface area that is available for reaction.
The answer is 10.81 g of boron.