yes substances Do react by mass
Answer:
The answer is option a. The evaporation of water from the skin
Explanation:
An endothermic reaction is any synthetic reaction that retains heat from its environment. The ingested energy gives the enactment energy to the reaction to happen.
No new bonds formed, no bonds broken in this example. water molecules go from liquid to vapour (gas ), intermolecular bond exist between polar (-OH) molecules and energy is required to break these bonds during the change from liquid to gas. So, it is endothermic .
Remaining three above examples are exothermic. combustion of gas releases energy(exothermic). burninig of the candle exothermic because the energy released from the oxygen into carbon dioxide and water.oxidation of iron also exothermic
Number 1.c
number 2.a
number 3.b
number 4.d
Answer:
The heat required to raise the temperature of 12g of water from 16 C to 21 C is 60 cal.
Explanation:
Calorimetry is the measurement and calculation of the amounts of heat exchanged by a body or a system.
There is a direct proportional relationship between heat and temperature. The constant of proportionality depends on the substance that constitutes the body as on its mass, and is the product of the specific heat by the mass of the body. So, the equation that allows calculating heat exchanges is:
Q = c * m * ΔT
where Q is the heat exchanged by a body of mass m, made up of a specific heat substance c and where ΔT is the temperature variation.
In this case, you know:
- Q=?
- c= 4.186
- m= 12 g
- ΔT=Tfinal - Tinitial= 21 °C - 16°C= 5 °C
Replacing:
Q= 4.186 *12 g *5 °C
Solving:
Q=251.16 J
Since 1 J is equal to 0.2388 cal, then the following rule of three can be applied: if 1 J is equal to 0.2388 cal, then 251.16 J to how many cal are?
cal= 59.98 ≅ 60
<u><em>The heat required to raise the temperature of 12g of water from 16 C to 21 C is 60 cal.</em></u>
The dissociation of both salts NaCl and CaCl₂ are as follows;
NaCl --> Na⁺ + Cl⁻
CaCl₂ --> Ca²⁺ + 2Cl⁻
the molar ratio of NaCl to Cl⁻ is 1:1
therefore number of NaCl moles is equal to number of Cl⁻ ions dissociated from NaCl
then number of Cl⁻ ion moles - 0.233 mol/L x 0.1000 L = 0.0233 mol
molar ratio of CaCl₂ to Cl⁻ ions is 1:2
1 mol of CaCl₂ gives out 2 mol of Cl⁻ ions.
number of CaCl₂ moles - 0.150 mol/L x 0.2500 L = 0.0375 mol
then the number of Cl⁻ ion moles - 0.0375 x 2 = 0.0750
total number of Cl⁻ ion moles = 0.0233 mol + 0.0750 mol = 0.0983 mol
volume of solution - 100.0 + 250.0 = 350.0 mL
concentration of Cl⁻ = 0.0983 mol / 0.3500 L = 0.281 M
concentration of Cl⁻⁻ is 0.281 M
