Answer:
-177.9 kJ.
Explanation:
Use Hess's law. Ca(s) + CO2(g) + 1/2O2(g) → CaCO3(s) ΔH = -812.8 kJ 2Ca(s) + O2(g) → 2CaO(s) ΔH = -1269.8 kJ We need to get rid of the Ca and O2 in the equations, so we need to change the equations so that they're on both sides so they "cancel" out, similar to a system of equations. I changed the second equation. Ca(s) + CO2(g) + 1/2O2(g) → CaCO3(s) ΔH = -812.8 kJ 2CaO(s) → 2Ca(s) + O2(g) ΔH = +1269.8 kJ The sign changes in the second equation above since the reaction changed direction. Next, we need to multiply the first equation by two in order to get the coefficients of the Ca and O2 to match those in the second equation. We also multiply the enthalpy of the first equation by 2. 2Ca(s) + 2CO2(g) + O2(g) → 2CaCO3(s) ΔH = -1625.6 kJ 2CaO(s) → 2Ca(s) + O2(g) ΔH = +1269.8 kJ Now we add the two equations. The O2 and 2Ca "cancel" since they're on opposite sides of the arrow. Think of it more mathematically. We add the two enthalpies and get 2CaO(s) + 2CO2(g) → 2CaCO3(s) and ΔH = -355.8 kJ. Finally divide by two to get the given equation: CaO(s) + CO2(g) → CaCO3(s) and ΔH = -177.9 kJ.
I would say D: 2 and 4.
The first line of the question is very important. X reacts with Y to form a gas.
For 2, we let the gas escape and measure the change in mass during the reaction.
For 4, we capture the change in volume of gas during the reaction.
1 does not work: some of the gas escapes through the cotton and the gas captured is not recorded correctly.
3 does not work: the gas is trapped and the mass balance does not record a change in mass.
Machines can be classified into two categories: Simple and Compound
A simple machine is a basic device used for applying a force to produce a certain outcome. for example: lever, wedge, inclined plane are all simple machines.
A compound machine is a combination of simple machines.
In the given example: Shovel is a compound machine which is a combination of wedge and lever.
Answer:
the volume of the hydrogen sample is greater than the volume of the helium sample.
Explanation:
Density=mass/volume
Now just plug each value in the given equation
For Helium
0.00018 g/cm3 = 1g/x
x= 5555.56 cm3
For hydrogen
0.00009gcm3=1g/x
x= 11111.11 cm3
This shows us that the volume of the hydrogen sample is greater than the volume of the helium sample.
I think this is correct but double check my work and ask others as well!