Each element... A. Has only one kind of atom B. Has only one kind of molecule C. Is made of rock D. All of the above

A. Has only one kind of atom

Explanation:

All forms of matter are composed of elements.

An element is a substance which cannot be broken down into simpler units or converted into other substances by ordinary chemical reactions. Each element is composed of only one kind of atoms which are unique to each element. There are three fundamental sub-particles present in atoms of elements; these are: protons, electrons and neutrons. An atom of an element differs from an atom of another element by its atomic number. The atomic number of an element is the number of protons present in the nucleus of the atom of that element. For example, hydrogen atoms has an atomic number of 1, while sodium atoms has an atomic umber of 11.

Atoms of the same element or different elements may combine together to form the molecules of a substance. For example, a molecule of hydrogen gas is made up of two atoms of hydrogen whereas a molecule of water is composed of two atoms of hydrogen and an atom of oxygen.

Elements can exist in any of the three physical states: solids, liquids or gases. For example, hydrogen exists as gas, mercury as a liquid, while gold exists as a solid.

when 25.0 ml of 0.700 mol/l naoh was mixed in a calorimeter with 25.0 ml of 0.700 mol/l hcl, both initially at 20.0 °c, the temperature increased to 22.1 °c. the heat capacity of the calorimeter is 279 j/°c.

the equation for the reaction is:

naoh + hcl → nacl + h₂o

moles of hcl = 0.0250 l hcl ×

0.700

mol hcl

1 l hcl = 0.0175 mol hcl

volume of solution = (25.0 + 25.0) ml = 50.0 ml

mass of solution = 50.0 ml soln ×

1.00

ml soln

= 50.0 g soln

δt=t2-t1

= (22.1 – 20.0) °c = 2.1 °c

the heats involved are

heat from neutralization + heat to warm solution + heat to warm calorimeter = 0

q1+q2+q3=0

nδh+mcδt+cδt=0

0.0175 mol ×

δh

+ 50.0 g × 4.184 j·g⁻¹°c⁻¹ × 2.1 °c + 279 j°c⁻¹ × 2.1 °c = 0

0.0175 mol ×

δh

+ 439.32 j + 585.9 j = 0

0.0175 mol ×

δh

= -1025.22 j

δh=1025.22j0.0175 mol= -58 600 j/mol = -58.6 kj/mol